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Question
The Sum of first five multiples of 3 is ______.
Options
45
55
15
75
Solution
The Sum of first five multiples of 3 is 45.
Explanation:-
The given sequence is 3, 6, 9,...
Here,
a = 3
d = 3
n = 5
Therefore,
`S_n = n/2(2a+(n-1)d)`
`S_5 = 5/2(2a+(5-1)d)`
`=5/2(2(3)+4(3))`
`=5/2(6+12)`
`=5/2(18)`
`=5(9)`
= 45
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