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