问题 解答题

一批零件,甲单独做8小时完成,甲做2小时后,甲、乙二人又合作了4小时完成任务,乙单独做完成这批零件需要几小时?

答案

乙的工作效率:

(1-1÷8×2)÷4-1÷8,

=(1-

1
4
)÷4-
1
8

=

3
4
÷4-
1
8

=

3
16
-
1
8

=

1
16

乙单独做完成这批零件需要的时间:1÷

1
16
=16(小时);

答:乙单独做完成这批零件需要

1
16
小时.

单项选择题
单项选择题

The following two questions refer to the following passage:

A prestigious private high school has made available to local families a tuition prepayment plan to ease the burden of paying the school’s hefty tuition when a student matriculates. The plan allows parents of children under three years old to reserve a spot for their child at the school by making a payment of one-fourth of the current annual tuition for the high school. The parents then make an identical payment every year for the next 15 years, and the student’s full four-year tuition is considered paid in full, regardless of how much the regular tuition payments have risen in the intervening years.

Under which of the following circumstances would it be advisable for parents to take part in the prepayment plan ?()

A. If the school assures parents that participation in the prepayment plan will be taken into consideration when the school admissions council makes decisions about which first-year students to admit to the school

B. If the parents are certain that their child will attend this high school, and if the rate of tuition increase would surpass the rate of return that the parents could earn if they invested the same 16 payments in interest-bearing investments of their own choosing

C. If the children of other parents who have taken part in the prepayment plan have been successful at the high school and gone on to enroll at Ivy League universities

D. If the parents feel that this high school will provide the best educational, athletic, and social experience that their child could receive

E. If the school can guarantee that its level of prestige at the time of the student’s matriculation will be as great as or greater than its current level