theachiever wrote:By what percent did the price of a book increase?

1.Ratio of book's original price to it's new price is 4:5.

2.Ratio of change in the book's price to it's new price is 1:5.

Target question: By what percent did the price of a book increase?

To find the percent change, we can use this formula:
% change = 100(change)/(original value)

Statement 1: Ratio of book's original price to its new price is 4:5
So, we can say that the original price is 4K, and the new price is 5K (for some value of K)
From this, we can conclude that the change in price is K (since 5K - 4K = K)
Now apply the formula: % change = 100(K)/(4K) = 25%
Since we can answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: Ratio of change in the book's price to its new price is 1:5
So, we can say that the change in price is N, and the new price is 5N (for some value of N)
From this, we can conclude that the original price can be either 4N (if the price increased) or 6N (if the price decreased)
However, the question tells us that the price increased, so we can conclude that original price is 4N
Now apply the formula: % change = 100(N)/(4N) = 25%
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

Answer = D

Cheers,
Brent