X = [IF] [ID] [OF] [EX] [WB]; Clock = 8ns
Y = [IF] [ID1] [ID2] [OF] [EX1] [EX2] [EX3] [EX4] [WB]; Clock = 8ns
For X:
Let number of instructions be 100.
70 inst. of CPI = 1, 30 inst. of CPI = 5
Thus Total Execution time = 70 x 1 x 8 + 30 x 5 x 8 = 1760 ns
Total Execution Time without pipeline = 100 x 22ns = 2200 ns
Thus Speedup(x) = 2200/1760 = 1.25
For Y:
Let number of instructions be 100.
70 inst. of CPI = 1, 30 inst. of CPI = 9
Thus Total Execution time = 70 x 1 x 8 + 30 x 9 x 8 = 2720 ns
Total Execution Time without pipeline = 100 x 51ns = 5100 ns
Thus Speedup(y) = 5100/2720 = 1.875
Therefore, Speedup(x)/Speedup(y) = 0.666 or 66.66%