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The first n multiples of 5 are 5, 10, 15, ... and their sum is 275.
Find the value of n.

Class 10AP Word ProblemsAlgebra — Sequences

A10
B11
C9
D12

Step-by-Step Solution

Sum = 5(1+2+...+n) = 5

x \frac{n ( n + 1 )}{2} = 275

, so

n (n + 1) = 110 = 10 \times 11

. Hence

n = 10

.

Answer: A) 10

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