Question

Find the sum of first 60 multiples of 3 ?

Answer 1

This is an AP 3,6,9...

1st term = 3.

60th term = 3 * 60

                  = 180.

Sum of the whole positive number is n(first +last)/2.

Sum of 1st 60 multiples = 60(3 + 180)/2

                                        = 60(183)/2

                                        = 30(183)

                                        = 5490.


Hope this helps!

Answer 2

Lets first look at the first three terms of this series.

3, 6, 9

To find the sum of an arithmetic series, there are two separate formulas. The one we will use is sn=n2(2a+(n−1)d)

n, or the number of terms, is 30. d, the common difference, is 3. a, the first term in the series is 3.

Plugging these numbers into the formula, we get:

s30=302(2(3)+(29)3)

s30=15(6+87)

s30=15(93)

s30=1395