lets assume 100 instruction out of which 78 are ALU and other instruction and 22 are load instruction
for 5 stage pipeline
number of cycle required 5 + 99 => 104
and time taken = 104n (lets assume each stage takes n seconds)
for 4 stage pipeline
the load instruction will divide into 2 instruction therefor 22 instruction become 44 instruction hence
total instruction = 78 (ALU and other instruction) + 44 (load instruction )
number of cycle required = 4 + 121 => 125
and time taken = 125n
speed up = 125n/104n => 1.2