单选题 Bob has 40 coins consisting only of dimes and quarters. If the number of dimes is 10 more than twice the number of quarters, what is the total value of the coins.
【正确答案】 D
【答案解析】dimes指10美分硬币，quarter指25美分硬币，假设quarters的数目为x，那么dimes的数目便是2x+10，根据题意有：x+2x+10=40，得到x=10，因此硬币总价值是30×0.1+10×0.25=5.5(美元)。