Summation notation

**Y-rag** · May 27th 2009, 06:58 PM

If I had 12 measurements: 30, -38, -70, -78, 32, 73, 49, -88, 29, 32, 42, 6, and they were labeled x1, x2, x3 etc, how would I find the following?

Find

.

I added all the numbers, and came up w/19. Then I took x1 which was 30 and added 49 to that and then multiplied that by 19 and came up w/1501 which is the wrong answer. Can anybody help me w/this? Thank you.

**Y-rag** · May 27th 2009, 07:02 PM

Originally Posted by Y-rag

If I had 12 measurements: 30, -38, -70, -78, 32, 73, 49, -88, 29, 32, 42, 6, and they were labeled x1, x2, x3 etc, how would I find the following?

Find

.

I added all the numbers, and came up w/19. Then I took x1 which was 30 and added 49 to that and then multiplied that by 19 and came up w/1501 which is the wrong answer. Can anybody help me w/this? Thank you.

Would this be 19+49= 68? Would that be the answer?

**VonNemo19** · May 27th 2009, 07:32 PM

$\sum_{i=1}^{12}(x_i+49)=\sum_{i=1}^{12}x_i+\sum_{i =1}^{12}49$

Now since $\sum_{i=1}^{12}49=49(12)$

and

$\sum_{i=1}^{12}x_i=30+(-38)+(-70)+(-78)+32+73+49+(-88)+29+32+42+6$

we have

$\sum_{i=1}^{12}(x_i+49)=30+(-38)+(-70)+(-78)+32+73+49+(-88)+29+32+42+6+[12(49)]<br /> <br />$

Can you handle it from here buddy?

**Y-rag** · May 27th 2009, 07:38 PM

VonNemo, I get 607. Does that seem like I handled it?

This is worse than learning to play the piano and I've never done that but I can guess how painful it would be.

**VonNemo19** · May 27th 2009, 07:50 PM

I'm getting 607. Try again. Always check your work, man.

**Y-rag** · May 27th 2009, 07:55 PM

I corrected myself after I sent the wrong number, I got 607 also. Dumb mistake on my part. Thank you immensely.

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