We are given a task which is split up into four parts:
P1 = 11%, P2 = 18%, P3 = 23%, P4 = 48%, which add up to 100%.
Then we say:
P1 is not sped up, so S1 = 1 or 100%, P2 is sped up 5×, so S2 = 500%, P3 is sped up 20×, so S3 = 2000%, P4 is sped up 1.6×, so S4 = 160%.
What is the overall Speedup for the task?
By using the formula P1/S1 + P2/S2 + P3/S3 + P4/S4, we find the running time is 0.4575 or a little less than ½ the original running time which we know is 1.
Therefore the overall speed boost is 1 / 0.4575 = 2.186 or a little more than double the original speed
Notice how the 20× and 5× speedup don't have much effect on the overall speed boost and running time when 11% is not sped up, and 48% is sped up by 1.6×.
This problem is adapted from the Amdahl's Law Wikipedia page