What is the % increase in population of City K from 1980 to 1990?
a. In 1970 population of K was 160,000
b. In 1980 population of K was 20% greater than 1970 and in 1990 population is 30% greater than in 1970
IMO: B
Population increase
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1 is useless because we don't have any info on 1980 or 1990.
2. Let x = population in 1970.
Population in 1980 will be 120% * x = 1.2x.
Population in 1990 will be 130% * x = 1.3x.
Now, say that from 1980 to 1990 the population grew by n%. This means that: 1.3x = (100 + n)/100 * 1.2x. As you can see, x can be very easiliy eliminated from both sides to get:
1.3 = (100 + n)/100 * 1.2
Solving for n is a breeze.
So 2 is indeed sufficient.
2. Let x = population in 1970.
Population in 1980 will be 120% * x = 1.2x.
Population in 1990 will be 130% * x = 1.3x.
Now, say that from 1980 to 1990 the population grew by n%. This means that: 1.3x = (100 + n)/100 * 1.2x. As you can see, x can be very easiliy eliminated from both sides to get:
1.3 = (100 + n)/100 * 1.2
Solving for n is a breeze.
So 2 is indeed sufficient.