Prove your math skills - Page 3

TBag · #21 10-12-2005, 08:49 PM

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Just put it in excel, drag the column down to how many rows there are, sum it up. Who needs math.

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and it took about 3 seconds

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Your sum formula probably left out the first cell (10).

Why am I not getting 1960 in Excel?

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1950

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theben · #22 10-12-2005, 08:52 PM

check the colored box! i do this all the time (leave out one cell in the grouping) it happens to the best of us

gol4pro · #23 10-12-2005, 10:09 PM

Pretty basic progression.

n1 = 10
n2 = 12
n(x) = 8 + (n)(2)

40 total terms.

n39 = 86
n40 = 88

88+10 = 98

98*(40/2) = 1960.

2+2 wannabe · #24 10-12-2005, 10:33 PM

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And what is the equation for this?

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I'm probably wrong here, but I'd guess it looks something like

39
[Sum]10 + 2n
n=0

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similar, but:

40
SUM (8+2i)
i=1

TomCollins · #25 10-12-2005, 10:43 PM

Last row has 39 * 2 + 10 = 88.

So 20 * (98) = 1960

PaultheS · #26 10-12-2005, 10:45 PM

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Last row has 40 * 2 + 10 = 90.

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Actually, the first row (out of 40 rows) has 10 seats, so the last row has 39 * 2 + 10 = 88 seats.

ttw22 · #27 10-12-2005, 10:51 PM

(Got this from high school physics)
You could visualize it as a graph of f(x) = 2x + 8
The area under the graph will give you the answer. It is made up of a rectangle of 8x40 and a right triangle with legs of 40 and 80. So you combine these two to find that the answer is 1920. That apparently disagrees with what everyone else is saying. I'll look into that.

AlphaWice · #28 10-12-2005, 10:51 PM

Why did 3 pages worth of people chime in just to do someone's homework?

RocketManJames · #29 10-12-2005, 10:59 PM

Here's another (lame) way to do it. Didn't see anyone do it this way, so I figure I'll throw up yet another way.

Sum of odd numbers is equal to the square of the number of odds. So, if we wanted to sum 1 + 3 + ... + 89, we have 45 odds. We now have 45^2 = 2025.

But, we over counted by 1 for each of the 40 values we needed so we need to subtract 40. Now we have 1985.

Next, we don't need 1 + 3 + ... + 9. So, we need to subtract 25, resulting in 1960.

Ya, lame way to do it, but it works.

-RMJ

pudley4 · #30 10-12-2005, 10:59 PM

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Why did 3 pages worth of people chime in just to do someone's homework?

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Because they all have to prove how big their e-peen is.