Question

vasu brought 12 notebooks for rs. 132. find the cost of 7 such notebooks..using direct and inverse proportion

Answer 1

It is a direct proportional relationship

⇒ buy more books = cost more money

Find the price of 1 notebook:

12 notebooks = Rs 132

1 notebook = 132 ÷ 12

1 notebook = Rs 11

Find the price of 11 notebook:

1 notebook = Rs 11

7 notebooks = 11 x 7 = Rs 77

Answer: 7 notebooks cost Rs 77

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ALTERNATIVE METHOD : USING FORMULA

Direct Proportional : y = kx

y = number of notebooks

x = cost of the notebooks

STEP 1: Solve k

y = kx

12 = k(132)

k = 12/132 = 1/11

STEP 2: Form equation:

Equation: y = 1/11 x

STEP 3: Find 7 notebooks

y = 7

y = 1/11 x

7 = 1/11 x

x = 7 x 11

x = Rs 77

Answer: 7 notebooks cost Rs 77

Answer 2

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