Thanks Achilles and Zulkarnain.
@ Achilles: I found a solution to a similar coin problem posted above. But somehow, I can't relate this to that. Only dimes have been asked here. Please go through the following:
Laura has 20 coins consisting of quarters and dimes. If she has a total of $3.05, how many dimes does she have?
(A) 3 (B) 7 (C) 10 (D) 13 (E) 16
Let D stand for the number of dimes, and let Q stand for the number of quarters. Since the total number of coins in 20, we get D + Q = 20, or Q = 20 - D. Now, each dime is worth 10 cents, so the value of the dimes is 10D. Similarly, the value of the quarters is 25Q = 25(20 - D). Summarizing this information in a table yields
Dimes Quarters Total Number D 20 - D 20 Value 10D 25(20 - D) 305
Notice that the total value entry in the table was converted from $3.05 to 305 cents. Adding up the value of the dimes and the quarters yields the following equation:
10D + 25(20 - D) = 305
10D + 500 - 25D = 305
-15D = -195
D = 13
Hence, there are 13 dimes, and the answer is (D).