Step-by-Step Prompts: How to Make AI Think Before It Answers

By Ravindra Bagale, trainer LinkedIn Last updated: 19 October 2026

Generative AI course · Chapter 7 · Estimated reading time: 14 minutes

In the last chapter you taught the AI a style by showing examples. Now we solve a different problem: wrong answers to questions with many steps, like a trip budget, a GST bill or a broken Excel formula. When you ask for the final answer in one go, the AI can jump to a wrong number that still looks confident. The fix is simple: ask it to work in steps, show each step, and check its own answer. You will also learn the Think buttons that ChatGPT, Gemini, Claude and Copilot now have, and when they are worth using. And as always, we check the final numbers ourselves in Excel.

What you will learn in this chapter

Why one-shot answers go wrong
The 5-step thinking prompt
Plan a trip budget step by step
Solve a GST bill and check it
Debug an Excel formula with AI
Use Think modes in 4 tools
Ask the AI to check itself
When step-by-step is not needed

1. Suppose a shop owner asks for the price without GST

Suppose we are Kiran, and we help in a bag shop in Pune. A customer paid ₹1,180 for a school bag, and the price includes GST at 18 %. The owner asks: "What is the price before GST, and how much is the GST?"

We ask the AI in one line:

A bag costs ₹1,180 including 18% GST. What is the GST amount?

Sometimes the AI (and many people) answer like this:

GST = 18% of ₹1,180 = ₹212.40

That is wrong. ₹1,180 already includes the GST, so 18 % must be taken on the price before GST, not on ₹1,180. Now we ask again, but this time we ask for steps:

A bag costs ₹1,180 including 18% GST.
Work step by step:
1. Write what we know.
2. Write the formula for the price before GST.
3. Calculate the price before GST.
4. Calculate the GST amount.
5. Check: price before GST + GST must equal ₹1,180.

Expected output (yours will be similar, not the same):

1. We know: price including GST = ₹1,180, GST rate = 18%.
2. Price before GST = price including GST ÷ (1 + 18/100) = 1,180 ÷ 1.18
3. Price before GST = ₹1,000
4. GST amount = ₹1,180 − ₹1,000 = ₹180
5. Check: ₹1,000 + ₹180 = ₹1,180. Correct.

The difference is not a smarter AI. The difference is that we asked it to show the path, so a wrong step has nowhere to hide. And because each step is visible, we can check it too.

2. Why step-by-step works

Remember from chapter 1: the AI writes one piece of text at a time, and each new piece depends on what it has already written. When it writes the steps first, the final answer is built on top of those steps. When it jumps straight to the answer, it has no steps to lean on.

The 5-step thinking prompt, from top to bottom

Use step-by-step prompts for:

Maths with more than one step (budgets, GST, discounts, EMIs, marks).
Plans with many parts (a trip, a study plan, an event).
Finding a mistake (a formula, a process, an argument).
Decisions with several options (which laptop, which course).

You do not need it for: rewriting a message, a simple fact question, or a short email.

3. The 5-step thinking prompt (copy and save)

[Your question]

Work step by step:
1. Write what we know (the facts and numbers).
2. Write what we need to find.
3. Plan the steps before solving.
4. Solve each step and show the working.
5. Check the final answer in a different way, and say if anything is uncertain.
Then give the final answer on one line that starts with "Final answer:".

The last line matters: you get a clear final answer plus all the working above it.

Ravindra Bagale's Tip

Students copy only the final number from the AI and skip the steps. The steps are the useful part. Read them like a teacher checks a student's notebook: is each line correct? If one step is wrong, tell the AI exactly which step, for example: "Step 3 is wrong: there are 4 people, not 3. Redo from step 3."

4. Worked example 1: a trip budget for 4 friends

Situation: suppose we are Aditya and 3 friends in Pune, planning a 3-night trip to Goa. We want the total budget and each person's share. (The fares and prices below are made up for practice. For a real trip, check the current fares on IRCTC and the stay's own website.)

Paste this prompt:

Role: You are a careful trip planner.
Task: Make a budget for our trip.
Context:
- 4 friends, Pune to Goa and back, by train, 3 nights, 3 full days in Goa.
- Train fare: ₹650 per person, each way.
- Hostel: ₹800 per person per night.
- Food: ₹600 per person per day.
- 2 rented scooters: ₹500 per scooter per day, for 3 days.
- Use only these numbers. Do not add other costs.
Work step by step:
1. Write each cost item with its formula.
2. Calculate each item.
3. Add them for the total.
4. Divide by 4 for each person's share.
5. Check the total in a second way (add each person's share 4 times).
Format: a table with columns Item, Formula, Amount (₹), then the total and the share per person.

Expected output (yours will be similar, not the same):

Item	Formula	Amount (₹)
Train	650 × 2 ways × 4 people	5,200
Hostel	800 × 3 nights × 4 people	9,600
Food	600 × 3 days × 4 people	7,200
Scooters	500 × 3 days × 2 scooters	3,000
Total		25,000

Share per person: ₹25,000 ÷ 4 = ₹6,250
Check: ₹6,250 × 4 = ₹25,000. Correct.
Final answer: total ₹25,000, ₹6,250 per person.

Check it in Excel

In A1 to A4 type Train, Hostel, Food, Scooters.
In B1 type =650*2*4, in B2 =800*3*4, in B3 =600*3*4, in B4 =500*3*2.
In B5 type =SUM(B1:B4). You should see 25000.
In B6 type =B5/4. You should see 6250.

Follow-up idea, in the same chat: What if we stay 2 nights and 2 full days instead of 3? Redo only the items that change, and say which ones changed. The train stays ₹5,200. Hostel becomes ₹6,400, food ₹4,800 and scooters ₹2,000, so the new total is ₹18,400, or ₹4,600 per person. Check it in Excel the same way.

5. Worked example 2: a GST bill with CGST and SGST

Situation: Kiran's shop sells 2 items to a customer in Maharashtra (the same state as the shop). Prices are before GST, and both items are at 18 %. (GST rates depend on the item. India's main GST rates since 22 September 2025 are 5 %, 18 % and 40 %. For a real bill, check the rate for your item on the CBIC GST rates page or with your CA.)

Paste this prompt:

Role: You are a careful billing assistant for a shop in Maharashtra.
Task: Make the GST bill.
Context:
- Item 1: school bag, 2 pieces, ₹1,000 each, before GST.
- Item 2: water bottle, 3 pieces, ₹250 each, before GST.
- GST rate for both: 18%.
- The customer is in Maharashtra, so split GST into CGST and SGST equally.
Work step by step:
1. Taxable value of each item (quantity × rate).
2. Total taxable value.
3. CGST and SGST rates (half of 18% each).
4. CGST and SGST amounts.
5. Grand total, and a check that taxable value + CGST + SGST = grand total.
Format: a table, then the totals.

Expected output (yours will be similar, not the same):

Item	Qty	Rate (₹)	Taxable value (₹)
School bag	2	1,000	2,000
Water bottle	3	250	750
Total taxable value			2,750

CGST at 9% = 2,750 × 9 ÷ 100 = ₹247.50
SGST at 9% = 2,750 × 9 ÷ 100 = ₹247.50
Grand total = 2,750 + 247.50 + 247.50 = ₹3,245
Check: 2,750 × 1.18 = ₹3,245. Correct.
Final answer: ₹3,245 (CGST ₹247.50 + SGST ₹247.50).

Follow-up: The same customer is now in Karnataka. What changes? A correct answer: the sale goes to another state, so instead of CGST and SGST there is IGST at 18 %, ₹495, and the grand total stays ₹3,245.

Check it in Excel

In B1 type =2*1000+3*250. You should see 2750.
In B2 type =B1*9%. You should see 247.5.
In B3 type =B1+2*B2. You should see 3245.
For the price-before-GST trick from section 1: =1180/1.18 gives 1000.

Ravindra Bagale's Tip

Students ask the AI "what is the GST rate on my product?" and put that rate on a real bill. GST rates depend on the exact item and they change. Use the AI to do and explain the calculation. Take the rate from the official CBIC page or your CA, and give it to the AI in the prompt.

6. Worked example 3: debug an Excel formula

Situation: suppose we are Sana, and we keep a price list for a stationery shop. Sheet Prices has product codes in column A and prices in column B. In another sheet, our formula finds the price of a code, but it gives the wrong price for some codes.

Our formula is:

=VLOOKUP(A2,Prices!A:B,2)

Paste this prompt:

Role: You are a patient Excel trainer.
Task: Find why my formula gives the wrong price for some product codes.
Context:
- My formula: =VLOOKUP(A2,Prices!A:B,2)
- Sheet Prices: column A has product codes like P-104, P-017, P-233 (not sorted), column B has prices.
- For some codes I get the price of a different product.
Work step by step:
1. Explain what each part of my formula does.
2. Find the part that causes the wrong price.
3. Give the fixed formula.
4. Give one more formula that does the same job.
5. Tell me how to test the fix on 3 codes.

Expected output (shortened, yours will be similar, not the same):

1. A2 is the code to find. Prices!A:B is the table. 2 means "return column 2" (the price).
   The 4th part is missing.
2. When the 4th part is missing, VLOOKUP uses approximate match. Approximate match
   expects column A to be sorted, and can return a nearby row. Your codes are not sorted,
   so it can return the price of a different code.
3. Fixed formula (exact match): =VLOOKUP(A2,Prices!A:B,2,FALSE)
4. Same job with XLOOKUP: =XLOOKUP(A2,Prices!A:A,Prices!B:B,"Not found")
5. Test: pick 3 codes, find their prices by eye in the Prices sheet, and compare
   with the formula result.

Test the fix yourself:
1. Change the formula to =VLOOKUP(A2,Prices!A:B,2,FALSE).
2. Pick 3 codes. Find each one in the Prices sheet with Ctrl+F.
3. Compare the price you see with the formula result. All 3 must match.
Second problem, same sheet: one code now shows #N/A. Ask the AI step by step again, and add: The code looks the same in both sheets. A common cause is an extra space at the end of the code. Test with =LEN(A2) in both sheets: if one shows 6 and the other 5, there is an extra space. Clean it with =TRIM(A2).

7. Think modes: the "think longer" buttons in each tool

All four tools now have a way to make the AI spend more time reasoning before it answers. These options were checked on each company's help pages in October 2026. Names and places move, so look for these words.

Tool	Look for	Notes
ChatGPT	Think	On the mobile app, open the + menu and select Think. OpenAI says it is rolling out on the web too
Gemini	Effort or thinking level: Low, Medium, High	Free users get Auto model selection: most prompts go to the fastest model, harder ones may go to a bigger model
Claude	Extended thinking	Listed on Claude's free plan for complex work
Copilot	Think Deeper	Tap the mode button (it may say Quick response) and choose Think Deeper. Microsoft says it can take up to about 10 seconds

When to use a Think mode:

Multi-step maths, like the GST bill.
Finding a mistake in a formula or a process.
Comparing many options with many rules.

When not to: a quick rewrite, a translation or a short email. A Think mode is slower and, on some plans, uses more of your limit.

Important: a Think mode does not make the answer automatically right. Still ask for steps, and still check numbers in Excel.

8. Ask the AI to check itself

After any important answer, add one of these follow-ups in the same chat:

Follow-up	What it does
`Check your answer step by step and list any mistakes.`	A second look at its own working
`Solve it again in a different way and compare.`	Catches a wrong method
`Which step are you least sure about, and why?`	Shows where you should check
`Which numbers did you assume that I did not give?`	Catches invented data

This does not replace your own check. But it often finds a mistake before you do.

9. Beginner mistakes and quick fixes

Mistake	What happens	Fix
Asking only for the final number	Confident but wrong answers	Ask for steps and a check
Not reading the steps	A wrong step goes unnoticed	Read each line; point to the wrong step
Taking 18 % of a price that already includes GST	GST too high	Price before GST = inclusive price ÷ 1.18
Taking the GST rate from the AI	Wrong rate on a real bill	Take the rate from CBIC or your CA
Using a Think mode for every small task	Slow answers, limit used up	Use it for multi-step problems only
Trusting the AI's fixed formula without a test	The sheet is still wrong	Test on 3 rows you check by eye
Letting the AI add costs you did not give	The budget does not match reality	"Use only these numbers"

10. Try at home

Try at home

Task 1: your own budget

Plan a small outing (a picnic, a birthday party, a short trip) with 4 or 5 cost items.
Ask for the budget with the 5-step thinking prompt.
Check the total in Excel with =SUM().

Task 2: the GST trap

Ask the AI in one line: "A phone cover costs ₹590 including 18% GST. What is the GST?"
Ask again with the 5-step prompt.
Check with =590/1.18 in Excel. (The price before GST is ₹500, and the GST is ₹90.)

Task 3: fix a formula

Make a small sheet with 5 unsorted product codes and prices.
Use =VLOOKUP(code,range,2) without the 4th part and see what happens.
Ask the AI step by step why, then fix it with FALSE or XLOOKUP.

Recap

In short

For questions with many steps, ask the AI to work step by step and show the working.
The 5-step prompt: what we know, what we need, plan, solve, check, then "Final answer:".
Read the steps and point to the exact step that is wrong.
Price before GST = inclusive price ÷ 1.18 at 18 %. Within a state, GST splits into CGST and SGST; to another state, it is IGST.
A missing 4th part in VLOOKUP means approximate match; use FALSE or XLOOKUP for exact match.
Think modes (Think, effort levels, extended thinking, Think Deeper) help with hard problems but do not guarantee a right answer.
Always check the final numbers in Excel.

Next time you ask AI anything with numbers, add the words "work step by step and check your answer". It is the cheapest accuracy upgrade you will ever get.

Previous chapter: Few-Shot Prompting: Teach AI with Examples (Copy-Paste Prompts)

Next chapter: Ask AI for Tables, Checklists and JSON: Structured Output Made Easy

Ravindra Bagale, trainer: linkedin.com/in/ravindra-bagale. The people, shops, trip fares, prices and product codes on this page are made up for learning. GST rates depend on the item; check the official CBIC rates or your CA for real bills. Tool options were checked on the official help pages on 19 October 2026 and can change. AI answers change every time, so your output will be similar, not the same.