CAMANISHPARMAR wrote:

The population of Town X on January 1, 2010, was 56 percent greater than the population of the same town on January 1, 2005. The population of Town X on January 1, 2015, was 75 percent greater than the population of the same town on January 1, 2010. What was the population of Town X on January 1, 2005?

(1) The population of Town X on January 1, 2015, was 21,840.

(2) The increase in the population of Town X from January 1, 2010, to January 1, 2015, was 4,880 greater than the increase in the population of Town X from January 1, 2005, to January 1, 2010.

let the population of town X be X in 2005..

so in 2010 it becomes 1.56X and in 2015 it becomes 1.75*1.56X..

so all the populations are in term of X

if you know population of any one of the year, you will get X

(1) The population of Town X on January 1, 2015, was 21,840.

so 1.75*1.56X=21840

we can get X

suff

(2) The increase in the population of Town X from January 1, 2010, to January 1, 2015, was 4,880 greater than the increase in the population of Town X from January 1, 2005, to January 1, 2010.

so 1.75*1.56X-1.56X=4880+1.56X-X

so you have one term free of variable and rest all terms in X, we can find X

Suff

D

we dont have to try to find the values. knowing that equation will give us a value, Move ahead

**Edit: **Edited typo

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1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372

2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html

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