问题
单项选择题
Kim bought a total of $2.65 worth of postage stamps in four denominations. If she bought an equal number of 5-cent and 25-cent stamps and twice as many 10-cent stamps as 5-cent stamps, what is the least number of 1-cent stamps she could have bought ？（）
A.5
B.10
C.15
D.20
E.25
答案
参考答案：C
解析：
设Kim购买了m张1美分的邮票，且购买了n张5美分的邮票，则她购买了n张25美分的邮票和2n张10美分的邮票，根据题意可得到下面的方程：
5n+25n+10×2n+m=265
→m=265-50n
要使y最小，就必须使n取最大值为5，得到m=15