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If the cost of a long-distance phone call is c cents for the first minute and 2/3 c cents for each additional minute, what is the cost, in cents, of a 10-minute call of this type?
A.5/3 c
B.6c
C.20/3 c
D.7c
E.23/3 c

A.5/3
B.6c
C.20/3
C.7c
E.23/3

【参考答案】

D
解析:若长途电话费为第一分钟收c美分,以后每增加一分钟,加收2/3 c美分,那么按这种计费方式打10分钟的电话需付多少钱(以美分为单位)?
解:本题的正确答案为(D)。由题意可得:c+(10-1)×2/3 c=7c
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