Test Index

RRB ALP CBT I 25 Nov 2024 Shift 1 Paper

Question : 8 of 75

Marks: +1, -0

The average of the first 25 multiples of 3 is:

Solution:

Concept:

The average of an arithmetic sequence of multiples equals the sum of the terms divided by the number of terms.

Explanation:

The first 25 multiples of 3 are

3, 6, 9, \dots, 75

Sum of the first

n

multiples of a number

a

is given by:

\text{Sum} = a \times \frac{n(n+1)}{2}

Here,

a = 3

and

n = 25

\text{Sum} = 3 \times \frac{25 \times 26}{2} = 3 \times 325 = 975

Average is calculated as:

\text{Average} = \frac{\text{Sum}}{n} = \frac{975}{25} = 39

So, the average of the first 25 multiples of 3 is 39.

Answer:

Option A: 39

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