[求助]GWD 5 两道吃不准的 数学题

GWD 5

Q21: (我选的是C，尽管条件给了unoccupied seats, 但通过总的seats数减去unoccupied seats,一样能求得occupied的呀)

Theater M has 25
rows with 27 seats in each row.  How many
of the seats were occupied during a certain show?

(1)   During the show, there was an average
(arithmetic mean) of 10 unoccupied seats per row for the front 20 rows.

(2)   During the show, there was an average
(arithmetic mean) of 20 unoccupied seats per row for the back 15 rows.

Answer:   E ?

Q28: (如果设 the amount of his income in this
year = 1 的话，我能得到E这个结果。不明白的是，如果设其我1 合理吗？)

This year Henry will save a certain amount of his income,
and he will spend the rest.  Next year
Henry will have no income, but for each dollar that he saves this year, he will
have 1 + r dollars available to
spend.  In terms of r, what fraction of his income should Henry save this year so that
next year the amount he was available to spend will be equal to half the amount
that he spends this year?

Answer: E            1/(2r+3)