The answer is 25%
(1)
If 64 is 100%, 48 is how much percent:
64 : 100% = 48 : x
x = 100% * 48 : 64
x = 75
(2)
Percent of decrease is:
100% - x = 100% - 75% = 25%
Megabyte difference = 96 - 24 = 72
time difference = 1:15 - 1:10 = 15 min.
Download rate would be: 72 / 15 = 4.8
So, Your Answer would be 4.8 mb/min
Hope this helps!
