The Testmaker here is trying to confuse the reader to complicate the math. However, if we conceptually understand the nature of range, we can see the math is fairly simple.
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The problem begins with the notion of 100 multiples of 7 greater than 70. Naturally, the first multiple would be 77, the second multiple would be 84, etc. In other words, the Nth multiple of N greater than 70 could be calculated with the equation 70 + 7(N). To calculate the range, we would subtract the 100th multiple from the 1st multiple:
[(70 + 7(100)] - [70 + 7(1)]
7(100) - 7(1)
700 - 7
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There is an even easier solution, however. As we can see, the two values of 70 cancel. This underscores a fundamental notion of range: if we add the same value to every element in a set, this doesn’t change the range. If we recognized this concept from the very beginning, the math to this problem becomes even simpler. We simply need to subtract the 100th multiple of 7 from the 1st multiple of 7 to get our answer (700 – 7 = 693).
The answer is “A”.
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