Hi Newaz111,
TESTing VALUES (the approach that Brent used) is a great approach for these types of questions. You can also solve this question with Algebra...
We have 3 pounds of raisins and 4 pounds of nuts. We're told that a pound of nuts costs 3 TIMES as much as a pound of raisins, so we can call the prices:
X = price per pound of raisins
3X = price per pound of nuts
The total price of this mixture would then be:
3(X) + 4(3X) = 3X + 12X = 15X
We're asked for the total cost of the raisins divided by the total cost of the mixture:
Total cost of raisins: 3X
Total cost of he mix: 15X
3X/15X = 1/5
Final Answer: D
GMAT assassins aren't born, they're made,
Rich