A man and boy problem

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gmatrant: Master | Next Rank: 500 Posts; Posts: 416; Joined: Wed Oct 03, 2007 9:08 amFollowed by: 1 member; Thanked: 10 times

by gmatrant » Sat Sep 06, 2008 7:22 am

A man and a boy together dig 600kg of earth in an hour working independently but simultaneously. How long would the man take working alone?

1) The man moves 200 ks/h more than the boy
2)The boy works twice as long as the man

Ans: [spoiler] A, why wouldnt (2) also be able to give an answer. shouldnt it be D.[/spoiler]

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Source: Beat The GMAT — Data Sufficiency | Sat Sep 06, 2008 7:22 am

sumithshah: Master | Next Rank: 500 Posts; Posts: 165; Joined: Wed May 28, 2008 11:25 pm; Thanked: 9 times; GMAT Score:730

by sumithshah » Mon Sep 08, 2008 10:00 pm

Agree with you - wher is this from

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pseudononymous: Senior | Next Rank: 100 Posts; Posts: 33; Joined: Fri Sep 05, 2008 6:40 am; Thanked: 1 times

by pseudononymous » Wed Sep 10, 2008 6:35 am

(2) Doesn't tell you their digging rate. A man digging 599kg/hr would finish faster than a man digging 1kg/hr.

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mim3: Senior | Next Rank: 100 Posts; Posts: 58; Joined: Fri Apr 04, 2008 12:36 pm; Thanked: 4 times; GMAT Score:680

by mim3 » Wed Sep 10, 2008 10:58 am

I thought it was D initially, but I think it's A now.

Looking at Statement 2:
From the stem, we know how long they worked together (1 hr) and statement 2 gives us the ratio of the time they spent working individually (1/3:2/3) but as pseudononymous pointed out, we can't determine the indvidual rates. There could be multiple values that satisfy the equation.

For example, let x=the man's rate and y=the boys rate. We know how long they worked individually (man=1/3hr. boy=2/3hr). So, the equation would be:

(1/3)x+(2/3)y= 600

(x,y) could = (300,750), (1200, 300), (600,600), ect...

Thus, it's insuffient and the answer is A.

Can we get an expert to weigh in on this one?

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Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members; Location: Toronto; Thanked: 1710 times; GMAT Score:800

by Stuart@KaplanGMAT » Wed Sep 10, 2008 12:43 pm

To be honest, I don't even understand statement (2).

The original info says:

A man and a boy together dig 600kg of earth in an hour working independently but simultaneously.

And then (2) says:

2)The boy works twice as long as the man

How can they work independently but simultaneously for an hour and the boy work twice as long as the man?

Either statement (2) has been misquoted or this is just a really bad question. What's the source?

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

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canuckclint: Master | Next Rank: 500 Posts; Posts: 154; Joined: Tue Aug 26, 2008 12:59 pm; Location: Canada; Thanked: 4 times

by canuckclint » Thu Sep 11, 2008 9:34 pm

Stuart Kovinsky wrote:To be honest, I don't even understand statement (2).

How can they work independently but simultaneously for an hour and the boy work twice as long as the man?

Easy, they work independently but at the same time with each other.
Think synchronized swimming?

Last edited by canuckclint on Thu Sep 11, 2008 9:40 pm, edited 1 time in total.

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canuckclint: Master | Next Rank: 500 Posts; Posts: 154; Joined: Tue Aug 26, 2008 12:59 pm; Location: Canada; Thanked: 4 times

by canuckclint » Thu Sep 11, 2008 9:37 pm

The answer is A as stated.

1/timeMan + 1/timeBoy = 1/1
1/1 becase 1/timeTotal

workBoy = 200kg + workMan
workMan + workBoy = 600kg
Can find work done by both people here.

And then just divide workMan/1 hour.

Easy enough and not Ambiguous.

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Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members; Location: Toronto; Thanked: 1710 times; GMAT Score:800

by Stuart@KaplanGMAT » Sat Sep 13, 2008 9:23 pm

canuckclint wrote:
Stuart Kovinsky wrote:To be honest, I don't even understand statement (2).

How can they work independently but simultaneously for an hour and the boy work twice as long as the man?

Easy, they work independently but at the same time with each other.
Think synchronized swimming?

If they work at the same time as each other, how does the boy work twice as long as the man?

In most GMAT work problems, we see the phrase "independently but simultaneously", or something very similar - I have no problem with that part. I just don't see how they can work simultaneously for different amounts of time - that's a contradiction.

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