Bunuel wrote:

James can eat 25 marshmallows is 20 minutes. Dylan can eat 25 in one hour. In how much time will the two eat 150 marshmallows?

A. 40 minutes.

B. 1 hour and 30 minutes.

C. 1 hour.

D. 1 hour and 40 minutes.

E. 2 hours and 15 minutes.

The combined rate, in marshmallows per minute, of James and Dylan is 25/20 + 25/60 = 5/4 + 5/12 = 15/12 + 5/12 = 20/12 = 5/3.

To eat 150 marshmallows, it will take them 150/(5/3) = (150 x 3)/5 = 30 x 3 = 90 minutes = 1 hour and 30 minutes.

Alternate solution:

Since James can eat 25 marshmallows in 20 minutes, he can eat three times as many in an hour. Thus he can eat 75 marshmallows in one hour. Therefore, the combined rate, in marshmallows per hour, of James and Dylan is 75 + 25 = 100.

So it takes them 150/100 = 1.5 hours = 1 hour and 30 minutes, to eat 150 marshmallows.

Answer: B

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