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help on these please

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help on these please

by xcise_science » Mon Dec 03, 2007 9:20 pm
please help out on these,
thanks

Image
answer is D

For this, i see now how the answer is close to but not quite 400, but is this something that would have to be worked out? If so, can someone show me how the answer is 357?

Image

Thanks
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by sujaysolanki » Tue Dec 04, 2007 12:27 am
The first one is geometric sequence

Sn = a (1-r^n)/1-r

where a = 1/2 r = -1/2 and n = 10

So its between 1/4 and 1/2 thats D



The second one uses the length of the arc

= x/360*2 pi * r
We know x = 90 and r = 100 so
length = 100 + 100 + length that is 157 approx C
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by xcise_science » Tue Dec 04, 2007 7:51 am
can you show me how you solved this:
Sn = a (1-r^n)/1-r

where a = 1/2 r = -1/2 and n = 10

So its between 1/4 and 1/2 thats D

for the 2nd question, how did you get arc =157?
I thought the formula for the arc length was:
(central angle/360)=(arc/circumference)?


thanks
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by Suyog » Tue Dec 04, 2007 12:29 pm
1. https://www.beatthegmat.com/integer-gmat ... html#23503

2. r = 100

The perimeter of the circle = 2 * pi * r = 2 * 3.14 * 100 = 628
Since the Angle given is 90, the length of the Arc will be 628/4 = 157

Now the Length of the fence = 100 + 100 + 157 = 357
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