# The sum of first five multiples of 3 is ______. - Mathematics

MCQ
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The sum of first five multiples of 3 is ______.

• 45

• 55

• 65

• 75

#### Solution

The sum of first five multiples of 3 is 45.

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]  .....[because S_n = n/2 {2a + (n - 1)d}]

= 5/2 [2 xx 3 + 4 xx 3]

= 5/2 (6 + 12)

= 5 xx 9

= 45

Concept: Sum of First n Terms of an A.P.
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#### APPEARS IN

NCERT Mathematics Exemplar Class 10
Chapter 5 Arithematic Progressions
Exercise 5.1 | Q 18 | Page 47
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