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Lesson 1, Topic 1
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# 2EM 1.2 Exercise Question 5

The illumination, $$I$$ units, of a bulb varies inversely as the square of the distance, $$d$$ metres.
Given that the illumination is $$9$$ units when the distance is $$2$$m,

(a)

express $$I$$ in terms of $$d$$,

(b)

find the percentage change in the illumination of the bulb which is required to reduce the distance of the bulb to $$\frac{1}{5}$$ of its original value.