$$E(t) = {A^2}{e^{ - \alpha t}}$$ ...... (i)

$$\alpha$$ = 0.2 s^$$-$$1

$$\left( {{{dA} \over A}} \right) \times 100 = 1.25\% $$

$$\left( {{{dt} \over t}} \right) \times 100 = 1.50$$

$$ \Rightarrow (dt \times 100) = 1.5t = 1.5 \times 5 = 7.5$$

Differentiating on both sides of equation (i), we get

$$ d \mathrm{E}=(2 \mathrm{~A} d \mathrm{~A}) e^{-\alpha t}+\mathrm{A}^2 e^{-\alpha t}(-\alpha d t) $$

Dividing throughout by $\mathrm{E}=\mathrm{A}^2 e^{-\alpha t}$

$$ \frac{d \mathrm{E}}{\mathrm{E}}=\frac{2}{\mathrm{~A}} d \mathrm{~A}+\alpha d t $$

(Considering worst possible case)

$$\therefore$$ $$\left( {{{dE} \over E}} \right) \times 100 = 2\left( {{{dA} \over A}} \right) \times 100 + \alpha (dt \times 100)$$

$$ = 2(1.25) + 0.2(7.5)$$

$$ = 2.5 + 1.5$$

$$ = 4\% $$