Concept 2 of 7
Unitary Method: Value of One
Today's big idea
Divide to find what one unit is worth, then multiply up to the number you need.
Going from cost back to quantity divides by the unit price rather than multiplying.
How it works
👀 What's going on?
Nine notebooks cost a certain amount and you need the price of four. Jumping straight from nine to four is awkward. Going through one is easy.
💡 Here's the trick
Look at the row above. Everything passes through the value of a single unit. Divide to find what one costs, then multiply up to whatever number you actually want.
🪄 How to do it
- 1.Read the given total off the row above.
- 2.Divide it by the number of units, to get the value of one.
- 3.Multiply that by the number of units you need.
✍️ Try it
If 7 pencils cost 91 rupees, what do 4 cost? Then: if 6 metres of rope cost 54 rupees, how much rope does 36 rupees buy?
One pencil is 91 divided by 7, which is 13, so 4 cost 52 rupees. One rupee buys 6 divided by 54 of a metre, so 36 rupees buys 4 metres.
⚠️ Watch out
You might be thinking you always divide first and multiply second. Check which way the question runs. Going from cost to quantity divides by the price of one, rather than multiplying by it.
🌟 Why this matters
Comparing two pack sizes in a shop is exactly this, and it is how you tell which one is genuinely cheaper.
Exam tip: Write the value of one on its own line, so you never lose it midway.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“6 notebooks cost ₹90. How much do 4 notebooks cost?”
- 1
Step 1 — find ONE
90 ÷ 6 = 15
- 2
Step 2 — scale up
15 × 4 = 60
- 3
Answer ✓
₹60
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
Step 1: divide to find the value of ONE. Step 2: multiply by the quantity you need.
SHOP · ROUND 1 OF 3
6 apples = ₹48
Step 1 — divide to find ONE: ₹48 ÷ 6 = ?
Quick check
✅ VERIFICATION
If 9 identical books cost 306 rupees, what do 4 of them cost?
⚡ Finish the activity above first to answer.
Keep going!
Up next: Percentage of a Quantity
Convert % to fraction, then multiply.