Hi dferm,
There's a really quick way to solve these. Note that the average of all the even numbers between 100 and 200 is going to be about 150. Then, note that we have about 50 even numbers between 100 and 200.
So, if we take 150 * 50, we get 7500, which is close to the right answer (close enough!).
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GMAT Prep?? (Sum of even)
Source: Beat The GMAT — Problem Solving |
AP can be easily used:
n/2 [2a + (n-1)d]
n=Total even numbers between 102 & 200 = 50
a=first term =102
d=2
=>25 [204+(49)2]
=>25[302]
=>7550
n/2 [2a + (n-1)d]
n=Total even numbers between 102 & 200 = 50
a=first term =102
d=2
=>25 [204+(49)2]
=>25[302]
=>7550
We got the formula to get the sum of even integers:
S = (a1 + an)x(number of integers)/2
Apply to this question :
a1=102; an=200
number of integers = ((200-102)/2) + 1 = 50
S= (102+200)x50/2 = 7550
S = (a1 + an)x(number of integers)/2
Apply to this question :
a1=102; an=200
number of integers = ((200-102)/2) + 1 = 50
S= (102+200)x50/2 = 7550
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