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If x is equal to the sum of the even integers from 40 to 60 [#permalink]
03 Jul 2009, 19:07

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25% (01:38) wrong based on 151 sessions

If x is equal to the sum of the 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?

Re: If x is equal to the sum of the even integers from 40 to 60 [#permalink]
03 Jul 2009, 19:47

Step 1 (y) - No of even numbers from 40-60 = 11

Step 2 (x) - Sum of those 11 nos is given by the formula - (F+L)*N/2 F= 40 L = 60 N =11 Therefore ==> 550

x+y = 550+11 = 561

tejal777 wrote:

if x is equal to the sum of the 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? 550 551 560 561 572

Guys I applied the formula for "sum of consecutive evn nos." but i am going wrong somewhere.Pease help. y=11 x=sum of consecutive even integers=n(n+1) where n= 1st even+last even/2 -1

Therefore,here n=40+60/2-1=50-1=49 So,x=49 x 50 =2450 Hence, x+y=2450+11=2461??!??!

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Re: If x is equal to the sum of the even integers from 40 to 60 [#permalink]
07 Jul 2009, 02:57

thanks guys i got the answer but I still dont know where im going wrong!!am i following the formulae wrong??please refer to link below from where i got the formula:

Re: If x is equal to the sum of the even integers from 40 to 60 [#permalink]
19 Jul 2010, 23:58

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If x is equal to the sum of the 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?

A. 550 B. 551 C. 560 D. 561 E. 572

Last edited by Bunuel on 24 Oct 2014, 02:14, edited 2 times in total.

Re: If x is equal to the sum of the even integers from 40 to 60 [#permalink]
20 Jul 2010, 00:50

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xmagedo wrote:

If x is equal to the sum of the 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? a 550 b 551 c 560 d 561 e 572

Sum of the even integers from 40 to 60 inclusive is \(x=\frac{40+60}{2}*11=550\). Even integers represent evenly spaced set, the sum of the terms in evenly spaced set is: mean, which is the average of the first and the last terms, multiplied bythe # of terms;

Re: If x is equal to the sum of the even integers from 40 to 60 [#permalink]
20 Jul 2010, 05:38

IMO D

xmagedo wrote:

If x is equal to the sum of the 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? a 550 b 551 c 560 d 561 e 572

pleas, someone help me with this !

Solution:

The number of even integers from 40 to 60 inclusive = 11 (40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60) Sum of integers = 550

Thus, total = 550 + 11 = 561 _________________

Gotta hit the 700 score this time... 3rd time lucky ! Give me some kudos... Like you, even I need them badly

Re: If x is equal to the sum of the even integers from 40 to 60 [#permalink]
20 Jul 2010, 23:15

xmagedo wrote:

If x is equal to the sum of the 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? a 550 b 551 c 560 d 561 e 572

pleas, someone help me with this !

Sum can be calculated using Arithmetic Progression

\(Sum = (n/2)(a+(n-1)*d)\)

In this case a(first term) = 40, d(difference) = 2(since nos are even)

\(n = ((60-40)/2)+1\) = 11

Thus sum = 550 (substituting the values)

and the number of terms have already been calculated as 11

Re: If x is equal to the sum of the even integers from 40 to 60 [#permalink]
29 Mar 2011, 06:41

1

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Another approach ('sum of pairs'): Step 1: 11 numbers Step 2: 40+60 = 42+58 = 100 (total 5 pairs, with exception of number 55 that does not have a pair) Step 3: 500 + 55 (the middle number with no pair)+ 11 = 561

Advantages: you don't need to know formulas nor you can make mistake in formulas

Re: If x is equal to the sum of the even integers from 40 to 60 [#permalink]
30 Mar 2011, 18:36

Expert's post

This is a perfect example of why you should not use formulas without understanding them properly. If you understand them, you will not make a mistake and will save time. The formula quoted by the original poster: n(n+1) is absolutely fine. But one needs to understand that n is the number of even terms starting from the first even term. (I discuss why this is so here: sum-of-even-numbers-68732.html#p849905)

Sum of even numbers from 40 to 60 using this formula will be: 30*31 - 19*20 = 10(3*31 - 19*2) = 550 Since number of terms is 11, required sum is 561

But, I would not use this formula for this question and would do it the way many of you have done: Average = 50 (it is the middle number), Number of terms = 11 (No formula again. Any 10 consecutive integers have 5 even and 5 odd numbers. 41 to 60 will have 10 even integers and 40 is the 11th one) Sum = 50*11 + 11 = 561 _________________

Re: If x is equal to the sum of the even integers from 40 to 60 [#permalink]
28 Sep 2012, 05:56

I agree with the answer responses above. I'd avoid fancy formulas and sequences if you're not familiar with them. Just step back and ask yourself " what is the total ("the sum"). Total is your average times your count. In this case, list out all the even numbers. Average is 50. There's 11 even integers (your count). 50 X 11 = 550. Add the 11. Boom. 561. I like this way too; list it out and split out the the numbers and do the math. Example: 40 + 0, 40 + 2, 40 + 4...and so forth. Count the number of 40's, which is 5, so 40 x 5 = 200, plus 2 + 4 + 6 + 8 = 20, totals 220. Do the same for the 50s. Remember to add the y. 561 is your total. Forced method is time consuming and causes errors.

Re: If x is equal to the sum of the even integers from 40 to 60 [#permalink]
28 Sep 2012, 06:07

Expert's post

xmagedo wrote:

If x is equal to the sum of the 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?

Re: If x is equal to the sum of the even integers from 40 to 60 [#permalink]
03 Feb 2015, 04:08

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