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
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What is the sum of all consecutive multiples of 8 between 400 and 600, inclusive?
This topic has expert replies
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 \(= \text{Number of multiples} \cdot \text{average}= 26 \cdot 500=13000\)
