Question

When the circumference of a toy balloon is increased from 40cm to 45cm its radius (in cm) is increased by:?

Answer 1

let the initial radius be a and final radius be b

so, increase in perimeter =45-40=5
$2\pi \: b - 2\pi \: a = 5 \\ 2\pi(b - a) = 5 \\ b - a = \frac{5}{2\pi} cm$

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