[問題]GWD 00-21

[panda]

21. On a recent trip,Mary drove 50 miles.What was the average speed at which she drove the 50 miles?

(1)She drove 30 miles at an average speed of 60 miles per hour and then drove 20 milesat an average speed of 50 miles per hour

(2)She drove a total 54 minutes

Answer:(D)

想請問為什麼不是(A)
我的想法：
由(1)得知
Sp=d/t, 60=30/t, t=1/2 hour = 30 minutes
50=20/t, t=2/5 hour = 24 minutes
total minutes = 30+24 =54

[shine822]

21. On a recent trip,Mary drove 50 miles.What was the average speed at which she drove the 50 miles?

(1)She drove 30 miles at an average speed of 60 miles per hour and then drove 20 milesat an average speed of 50 miles per hour

(2)She drove a total 54 minutes

Answer:(D)

想請問為什麼不是(A)
我的想法：
由(1)得知
Sp=d/t, 60=30/t, t=1/2 hour = 30 minutes
50=20/t, t=2/5 hour = 24 minutes
total minutes = 30+24 =54

A你求出來了很好 第一條件充份
第二個條件 不是更直接
只要用 50 miles/ 54 mins 就求出 speed 來
第二條件也充分

那當然是D囉~

[panda]

阿...腦筋一時轉不過來，問了蠢問題