We know that Execution time = CPI *$\frac{1}{Clock Rate}$ ………….(1)
P1 :
CPI = x(let)
Execution Time =y (let)
Put in equation 1
y = $\frac{x}{Clock rate}$ (given clock rate for P1 is 1 ghz)
y= $\frac{x}{1 Ghz}$
x = y*1ghz …...…….…….(2)
P2 :
CPI (given it is 20% more than P1) = x+x*$\frac{20}{100}$ =$\frac{120x}{100}$
Execution Time (given it is 25% less than P1) = y-y*$\frac{25}{100}$ =$\frac{75y}{100}$
Put in eq 1
$\frac{75y}{100}$ = $\frac{120x}{100}$ *$\frac{1}{Clock Rate}$
Clock Rate = $\frac{24x}{15y}$
Using eq 2
Clock Rate = $\frac{24 *y*1ghz}{15y}$
Clock Rate = 1.6 Ghz