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DS - Percent of

by karthikpandian19 » Thu Jun 28, 2012 11:38 pm
The neighborhood association planted 240 new trees last year. If there were no other changes to the neighborhood's tree population, how many of the new trees planted by the neighborhood association were elm trees?

1. Of all the trees in the neighborhood, 40 percent were elm trees at the end of last year.
2. At the beginning of last year, 20 percent of the trees in the neighborhood were elm trees.

*****W/o using the right calculation procedures, i can determine the answer. But let me know a method thru calculation*****
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by Birottam Dutta » Thu Jun 28, 2012 11:53 pm
Let initial number of trees be X.

So, after planting 240 trees, no. Of trees =240+X.

Using statement 1, we get number of elm trees at end of last year =0.4(240+X)---- this is insufficient.

Using statement 2, we get number of elm trees at starting of last year = 0.2 (X).---- this is insufficient.

Using both the statements together, number of elm trees in the new bunch of 240 = 0.4(240+X) - 0.2(X)

As we can see, we require the initial number of trees in order to determine the answer.

So both statement are also insufficient.

Answer E.

Hope this is correct.
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by Anurag@Gurome » Thu Jun 28, 2012 11:55 pm
karthikpandian19 wrote:The neighborhood association planted 240 new trees last year. If there were no other changes to the neighborhood's tree population, how many of the new trees planted by the neighborhood association were elm trees?

1. Of all the trees in the neighborhood, 40 percent were elm trees at the end of last year.
2. At the beginning of last year, 20 percent of the trees in the neighborhood were elm trees.
Looking at the statements I can guess that none of them are individually sufficient as none of them provides a definite relation between the number of total trees and number of elm trees. Hence, I'm going to analyze the problem taking both statements into consideration.

Say, at the beginning of last year, there were x trees in the neighborhood.
Hence, number of elm trees at the beginning of last year = 0.2x
Hence, number of elm trees by the end of last year = 0.4(x + 240)

Hence, number of elm trees planted by neighborhood association = 0.4(x + 240) - 0.2x = 96 + 0.2x

The correct answer is E.
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by karthikpandian19 » Thu Jun 28, 2012 11:56 pm
OA is E
karthikpandian19 wrote:The neighborhood association planted 240 new trees last year. If there were no other changes to the neighborhood's tree population, how many of the new trees planted by the neighborhood association were elm trees?

1. Of all the trees in the neighborhood, 40 percent were elm trees at the end of last year.
2. At the beginning of last year, 20 percent of the trees in the neighborhood were elm trees.

*****W/o using the right calculation procedures, i can determine the answer. But let me know a method thru calculation*****
Regards,
Karthik
The source of the questions that i post from JUNE 2013 is from KNEWTON

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by niketdoshi123 » Fri Jun 29, 2012 12:03 am
karthikpandian19 wrote:The neighborhood association planted 240 new trees last year. If there were no other changes to the neighborhood's tree population, how many of the new trees planted by the neighborhood association were elm trees?

1. Of all the trees in the neighborhood, 40 percent were elm trees at the end of last year.
2. At the beginning of last year, 20 percent of the trees in the neighborhood were elm trees.

*****W/o using the right calculation procedures, i can determine the answer. But let me know a method thru calculation*****
# of trees last year = x
total trees = x+240
40% were elm trees at the end of last year = .4*(x+240)=.4x+96
20% were elm trees at the beginning of last year = .2x

New elm trees planted = .4x+ 96- .2x = .2x+96

Hence we cannot find the exact number of new elm trees planted until we know the value of x
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