Mary takes 15 minutes to eat a plate of french fries.

Question

Mary takes 15 minutes to eat a plate of french fries. Ann takes 30 minutes to eat a plate of french fries. If Mary and Ann decide to eat fries, from the plate, each for a minute alternatively starting with Mary, how long will it take them to finish the plate, if each eats the french fries at her respective rate?
a. 8 mins
b. 10 mins
c. 18 mins
d. 20 mins
e. 45 mins

HolaMaven · Answer

Let the total fries in the plate are 30
Mary eats 2 fries per minutes
Ann eats 1 fries per minutes
so in 2 minutes they eat 3 fries.
To eat 30 fries they need 20 minutes

pushkarajnjadhav · Answer

Mary's rate 1/15
Ann's rate 1/30

so in 2 mins they both will eat 1/15+1/30 part of the french fries.
3/30 part of the french fries will be eaten in 2 mins, so in order to complete full plate of french fries, they will need 10 such cycles.
Therefore total time needed = 10*2 = 20 mins
Hence Answer is D.

Kudos if it helps.

generis · Answer

Use 30 fries (or any reasonable multiple of 15 and 30) to find out how many fries per minute each person eats. 1 plate, P = 30 fries. Substitute 30 fries, F, for 1 plate, P.

Mary =  \frac{1P}{15min}  =  \frac{30F}{15min} . Reduce.

M's rate =  \frac{2F}{1min}

A's rate:  \frac{1}{30}  =  \frac{30F}{30min}  =  \frac{1F}{1min}

There are 30 fries. Mary eats two fries in one minute. Ann eats one fry in 1 minute. But they don't eat during the same minute.

First minute: Mary eats two fries

Next minute: Ann eats one fry

So after two minutes, they have eaten 3 fries. How long will it take them to eat 30 fries?

\frac{3F}{2 min} = \frac{30F}{X mins}

3x = 60 
x = 20 minutes

Answer D

Kinshook · Answer

Marty eats 1/15 of a plate in a minute
Ann eats 1/30 of a plate in a minute

1/15 + 1/30 + 1/15 + 1/30 + ......... = 1
1/15 + 1/30 = 1/10 in 2 minutes
10* 1/10 in 2 * 10 minutes
=20 minutes

IMO D

bumpbot · Answer

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Mary takes 15 minutes to eat a plate of french fries.

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Mary takes 15 minutes to eat a plate of french fries.

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