$4)$ You analyse the performance of a fund, and find that the average return over a $2-$year period is $15\mathrm{.}3\%$ with standard deviation of $53\%,$ then over the following $1-$year period it is $7\mathrm{.}2\%$ with standard deviation of $8\%,$ and finally if you consider the whole $3-$year period you find the average return is $12\mathrm{.}6\%$ with standard deviation of $43\%($note: all returns and standard deviations are annualised$).$ The risk$-$free return is constant and equal to $5\%$ for both periods. Work out the Sharpe ratio for the two sub$-$periods separately, and then the whole period, and explain why the fund appears to be performing worse over the whole $3-$year period than in either of the two sub$-$periods. Discuss what implications your findings might have for fund performance evaluation.