The sum of first five multiples of 3 is

Options

A. 45
B. 55
C. 65
D. 75

Answer

A

Explanation

The first five multiples of 3 are 3, 6, 9, 12 and 15.
Here, first term, a = 3, common difference, d = 6 - 3 = 3 and number of terms, n = 5
` :. S_(5)=(5)/(2)[2a+ (5-1)d] " " [ :' S_(n)= (n)/(2){2a+(n-1)d}]`
` " " = (5)/(2)[2xx3+4xx3]`
` " " =(5)/(2)(6+12)=5xx9=45`