Question 894360
Lets say there are 100 workers working 8 hours a day
8*100 is 800 man work hours
if the number x works 10 hours for the same total of man work hours then 800/10=80 men working 10 hours
100-80=20 men cut 
20/100=20% reduction
You now are using 4/5 or 80% of the work force. You are using 1/5 or 20% less.