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# If x is equal to the sum of even integers from 40 to 60,

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If x is equal to the sum of even integers from 40 to 60, [#permalink]

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04 May 2008, 12:37
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

If x is equal to the sum of even integers from 40 to 60, inclusive, and y is the number of even integers from 40 to 60, inclusive, what is the value of x + y?

60 -40 = 20 + 1 (being inclusive), gives us 21 even numbers.

What i'm having trouble is finding a formula to add all even numbers from 40 to 60. Can someone help?
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04 May 2008, 12:48
You can use the Arithmetic Progression Sum formula-

S= n/2{2a+ (n-1)d}

here n=21, d=2
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05 May 2008, 06:01
If x is equal to the sum of even integers from 40 to 60, inclusive, and y is the number of even integers from 40 to 60, inclusive, what is the value of x + y?

60 -40 = 20 + 1 (being inclusive), gives us 21 even numbers.

What i'm having trouble is finding a formula to add all even numbers from 40 to 60. Can someone help?

(40+60)/2 = 50 --> 50

60-40+1 =21. Even integers so 11.

50*11=550

Now 550+11= 561.
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05 May 2008, 13:51
GMATBLACKBELT wrote:
If x is equal to the sum of even integers from 40 to 60, inclusive, and y is the number of even integers from 40 to 60, inclusive, what is the value of x + y?

60 -40 = 20 + 1 (being inclusive), gives us 21 even numbers.

What i'm having trouble is finding a formula to add all even numbers from 40 to 60. Can someone help?

(40+60)/2 = 50 --> 50

60-40+1 =21. Even integers so 11.

50*11=550

Now 550+11= 561.

That's a great strategy...

Or, you could work it out by hand, took me 45 seconds.

40+42+44+46+48+50 = 270
52+54+56+58+60 = 280

270+280 = 550

40-42-44-46-48-50-52-54-56-58-60 ===> 11 numbers

550+11 = 561
Re: GMAT Prep   [#permalink] 05 May 2008, 13:51
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