What is the total number of coins that Bert and Claire have?
(1) Bert has 50 percent more coins than Claire.
(2) The total number of coins that Bert and Claire have is between 21 and 28.
The stem asks us: B + C = TC, what is TC?
1) This tells us that B = 1.5 C, so now we have two unknowns: 2.5C = TC, insufficient
2) Gives us a range of possible values, so in itself 2 is insufficient because the value could be any of 6 values. Insufficient
1 + 2 : Look closely: given our equation from 1, TC must be a multiple of 5 (we cannot have fractions of coins), and given the restriction in 2, we only have ONE possible multiple of 5: 25...
So, TC = 25... Answer is C.