apple problem

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apple problem

by hareesh860 » Mon Feb 06, 2012 6:23 pm
a farmer has an apple orchard consisting of fuji and gala apple trees. due to high winds this year 10% of his trees cross pollinated. the no of trees that are pure fuji plus the cross pollinated ones totals 187, while 3/4 of his trees are pure fuji. how many trees are pure gala?

a)22 b)33 c)55 d)77 e)88
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by Anurag@Gurome » Mon Feb 06, 2012 7:06 pm
hareesh860 wrote:a farmer has an apple orchard consisting of fuji and gala apple trees. due to high winds this year 10% of his trees cross pollinated. the no of trees that are pure fuji plus the cross pollinated ones totals 187, while 3/4 of his trees are pure fuji. how many trees are pure gala?

a)22 b)33 c)55 d)77 e)88
Let the number of apple trees = N
10% of N = 0.1N of apple trees are cross-pollinated
Pure fuji = 3N/4
3N/4 + 0.1N = 187
0.85N = 187
N = 220
Pure Gala = N/4 - 0.1N = 55 - 22 = 33

The correct answer is B.
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by GMATGuruNY » Mon Feb 06, 2012 8:49 pm
hareesh860 wrote:a farmer has an apple orchard consisting of fuji and gala apple trees. due to high winds this year 10% of his trees cross pollinated. the no of trees that are pure fuji plus the cross pollinated ones totals 187, while 3/4 of his trees are pure fuji. how many trees are pure gala?

a)22 b)33 c)55 d)77 e)88
We can plug in the answers, which represent the number of pure gala trees.
Since 10% of all the trees cross-polinated, the total number of trees must be a multiple of 10.
Thus, when the correct answer choice (the number of pure gala trees) is added to 187 (the number of pure fuji trees plus the number of cross-polinated trees), the sum must be a multiple of 10.

Only B works: 33+187 = 220.

The correct answer is B.
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