If 9 notebooks cost ₹135, how much will 20 notebooks of the same type cost?
- AOption (a)
₹250
- BOption (b)
₹280
- COption (c)
₹320
- DOption (d)
₹300
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Correct answer
₹300
Why this answer is correct
Shortcut Trick
Use the Unitary Method directly by calculating the price per unit.
Cost of 1 unit = 135 ÷ 9 = ₹15.
Cost of 20 units = 20 × 15 = ₹300.
∴ The correct answer is ₹300.
Alternate Method
Given:
Cost of 9 notebooks = ₹135
Required quantity = 20 notebooks
Formula Used:
In Direct Proportion: (Price1 ÷ Quantity1) = (Price2 ÷ Quantity2)
Calculations:
⇒ 135 ÷ 9 = Price2 ÷ 20
⇒ 15 = Price2 ÷ 20
⇒ Price2 = 15 × 20
⇒ Price2 = ₹300
∴ The correct answer is ₹300.
Additional Information
Direct Proportion
Two quantities are in direct proportion if an increase in one leads to a corresponding increase in the other such that their ratio remains constant (x/y = k).
Unitary Method
The unitary method involves finding the value of a single unit first and then multiplying that value by the required number of units to find the total.
Ratio Application
The ratio of quantities (9 : 20) must be equal to the ratio of their costs (135 : x), which helps solve partnership and mixture problems as well.