What is the sum of all consecutive multiples of 8 between 400 and 600, inclusive?

[AAPL]

Economist GMAT

What is the sum of all consecutive multiples of 8 between 400 and 600, inclusive?

A. 8,000
B. 10,400
C. 12,500
D. 13,000
E. 15,000

The OA is D

[swerve]

Economist GMAT

What is the sum of all consecutive multiples of 8 between 400 and 600, inclusive?

A. 8,000
B. 10,400
C. 12,500
D. 13,000
E. 15,000

The OA is D

We can try as follows:

\(400\) is \(8\cdot 50\) and \(600\) is \(8\cdot 75\)

Average of \(400\) and \(600= 500\), extreme multiples of \(8\)

Number of multiples of \(8=75-50+1=26\)

Sum \(= \text{Number of multiples} \cdot \text{average}= 26 \cdot 500=13000\)