Answers

2016-07-09T21:13:12+08:00
This is an arithmetic sequence with first term 5 and last term 95 with a common difference of 5.
Solving for n, we get
95 = 5 + (n - 1)5
90 = (n - 1)5
18 = n - 1
n = 19

Using the data to solve for Sn
Sn = 19(95 + 5)/2
Sn = 19(100)/2
Sn = 19(50)
Sn = 950

The sum of the multiples of 5 from 1 to 100 is 950.
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