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

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Status: Math Tutor
Joined: 12 Aug 2017
Posts: 72

Kudos [?]: 29 [0], given: 13

WE: Education (Education)
Mary takes 15 minutes to eat a plate of french fries. [#permalink]

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02 Sep 2017, 11:53
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Question Stats:

53% (01:12) correct 47% (01:10) wrong based on 78 sessions

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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
[Reveal] Spoiler: OA

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Abhishek Parikh
Math Tutor
Whatsapp- +919983944321
Mobile- +971529685639
Website: http://www.holamaven.com

Kudos [?]: 29 [0], given: 13

Manager
Status: Math Tutor
Joined: 12 Aug 2017
Posts: 72

Kudos [?]: 29 [0], given: 13

WE: Education (Education)
Re: Mary takes 15 minutes to eat a plate of french fries. [#permalink]

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02 Sep 2017, 11:54
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
_________________

Abhishek Parikh
Math Tutor
Whatsapp- +919983944321
Mobile- +971529685639
Website: http://www.holamaven.com

Kudos [?]: 29 [0], given: 13

Manager
Joined: 12 Feb 2017
Posts: 64

Kudos [?]: 46 [0], given: 32

Mary takes 15 minutes to eat a plate of french fries. [#permalink]

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02 Sep 2017, 12:45
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

Kudos if it helps.

Last edited by pushkarajnjadhav on 03 Sep 2017, 22:14, edited 1 time in total.

Kudos [?]: 46 [0], given: 32

Director
Joined: 22 May 2016
Posts: 814

Kudos [?]: 264 [1], given: 552

Mary takes 15 minutes to eat a plate of french fries. [#permalink]

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03 Sep 2017, 15:09
1
KUDOS
HolaMaven wrote:
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

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

Kudos [?]: 264 [1], given: 552

Mary takes 15 minutes to eat a plate of french fries.   [#permalink] 03 Sep 2017, 15:09
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