Ans: D
Warren has exactly three types of coins in his piggy bank: $0.25, $0.50, and $1. If the number of $0.25 coins is 8, and the number of $0.50 coins is 4, how many $1 coins does he have?
Let's say that number of $1 coins is 'n' and we need to find the value of n.
We can write this equation from the question itself: (0.25)8 +(0.50)4 + (1)n = ?? this is just for the visual cues for us to get going with the question.
Now...
(1) The total value of the $1 coins in the piggy bank is 50% of the total value of all the coins.
from statement 1 we can write
(1)n = (1/2)[(0.25)8 +(0.50)4 + (1)n]
n = (1/2)[2+2+n] => n/2 = 2 => n =4
[Sufficient]
(2) The $1 coins make up 25% of the total number of coins in the piggy bank.
from statement 2 we can write (25%=1/4)
n = (1/4) (8+4+n) => 4n = 12+n => 3n =12=> n = 4
[Sufficient]
Both statements alone are sufficient to answer the question.