Bunuel
A town has a population growth rate of 10% per year. The population in 1990 was 2000. What was the population in 1992?
(A) 1600
(B) 2200
(C) 2400
(D) 2420
(E) 4000
Method I - calculate each "step" in the percent increase, using (original #) + (percentage of that #) = new total
1. 1990, population is 2,000
2. 1991, population increases by 10% of 2,000.
Ten percent of 2000 is 200.
Increase = 200 + 2,000 = 2,200 (new total)
3. 1992, population increases by another 10%, this time of 2,200.
Ten percent of 2,200 is 220.
Increase of 220 + 2,200 = 2,240
By 1992 the population has grown to 2,240
Method II - multiply the multipliers, then multiply by original value
1. A 10% increase has a multiplier of 1.1. That percent increase happens twice.
2. (1.1)*(1.1) = 1.21
3. 1.21 * 2,000 = 2,240
[Obviously, you can also simply multiply 1.1 * 1.1 * 2000.]