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If Sally can paint a house in 4 hours, and John can paint [#permalink]
02 Nov 2012, 09:46

00:00

A

B

C

D

E

Difficulty:

5% (low)

Question Stats:

99% (01:33) correct
1% (00:00) wrong based on 69 sessions

If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?

A. 2 hours and 24 minutes B. 3 hours and 12 minutes C. 3 hours and 44 minutes D. 4 hours and 10 minutes E. 4 hours and 33 minutes

Re: need some help [#permalink]
02 Nov 2012, 10:16

Hello...

Sally can paint a house in 4 hours; Which means in 1 hour she can paint 1/4th of the house. John can paint the same house in 6 hours. Which means in 1 hour she can paint 1/6th of the house.

Together in 1 hour they can paint: - 1/4 + 1/6 = 5/12th of the house.

Total Hours for painting the house together will be 12/5 = 2.4 Hours.

Re: need some help [#permalink]
02 Nov 2012, 10:25

1

This post received KUDOS

shrinivas280390 wrote:

Hello...

Sally can paint a house in 4 hours; Which means in 1 hour she can paint 1/4th of the house. John can paint the same house in 6 hours. Which means in 1 hour she can paint 1/6th of the house.

Together in 1 hour they can paint: - 1/4 + 1/6 = 5/12th of the house.

Total Hours for painting the house together will be 12/5 = 2.4 Hours.

Re: need some help [#permalink]
02 Nov 2012, 12:11

MariaF wrote:

shrinivas280390 wrote:

Hello...

Sally can paint a house in 4 hours; Which means in 1 hour she can paint 1/4th of the house. John can paint the same house in 6 hours. Which means in 1 hour she can paint 1/6th of the house.

Together in 1 hour they can paint: - 1/4 + 1/6 = 5/12th of the house.

Total Hours for painting the house together will be 12/5 = 2.4 Hours.

Hence Answer A

Thanks a lot I really made a stupid mistake :/

It'd be interesting how to use elimination techniques solving this problem?

Re: need some help [#permalink]
02 Nov 2012, 12:17

MariaF wrote:

Guys, help me please to solve this easy problem. I think I just make a stupid mistake If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?

A. 2 hours and 24 minutes B. 3 hours and 12 minutes C. 3 hours and 44 minutes D. 4 hours and 10 minutes E. 4 hours and 33 minutes

Re: need some help [#permalink]
02 Nov 2012, 12:22

RJSPO wrote:

MariaF wrote:

Guys, help me please to solve this easy problem. I think I just make a stupid mistake If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?

A. 2 hours and 24 minutes B. 3 hours and 12 minutes C. 3 hours and 44 minutes D. 4 hours and 10 minutes E. 4 hours and 33 minutes

Time taken will be = x*y/x+y = 4*6/4+6 [ A]

Nice trick, I have to remember it, x*y/(x+y) and if it would be three workers is it equal x*y*z/(x+y+z)?

Re: need some help [#permalink]
02 Nov 2012, 12:30

actleader wrote:

RJSPO wrote:

MariaF wrote:

Guys, help me please to solve this easy problem. I think I just make a stupid mistake If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?

A. 2 hours and 24 minutes B. 3 hours and 12 minutes C. 3 hours and 44 minutes D. 4 hours and 10 minutes E. 4 hours and 33 minutes

Time taken will be = x*y/x+y = 4*6/4+6 [ A]

Nice trick, I have to remember it, x*y/(x+y) and if it would be three workers is it equal x*y*z/(x+y+z)?

No, for 3 workers it will be quite a complicated formula : x*y*z/xy+yz+zx Better to use reciprocal formula for other cases

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