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by mjjking » Tue Mar 10, 2009 11:47 am
Guys, how do I solve this??

What is the sum of all the multipl of 7 between 100 and 200?

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by shulapa » Tue Mar 10, 2009 12:00 pm
In order to find the value of the sum of series we can use this equation:

(Series' average)*(number of elements) = Sum

In this case we can look at the question as a series of the multiplies of 7 from 105 to 196. Thus, average = (105 + 196)/2 = 150.5
number of elements = (196 - 105)/7 + 1 = 14

Therefore, SUM = 14*150.5 = 2107.
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by dendude » Tue Mar 10, 2009 5:41 pm
OR,
The lowest multiple of 7 is 105 and the highest multiple of 7 is 196
7*15 = 105
7*28 = 196

The sum required is,
7*15 + 7*16 + 7*17 + ....... + 7*28
= 7(15+16+17+..........28)

Find the sum of the AP formed and multiply it by 7
Sum = 301 * 7 = 2107
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