When Tom works alone he chops 2 lb. salad in 3 minutes...

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BTGmoderatorLU: Moderator; Posts: 2544; Joined: Sun Oct 15, 2017 1:50 pmFollowed by: 6 members

by BTGmoderatorLU » Fri Jan 19, 2018 6:50 am

When Tom works alone he chops 2 lb. salad in 3 minutes, and when tammy works alone she chops 3 lb. salad in 2 minutes. They start working together, and after some time finish chopping 65 lb. of salad. Of those 65 lb., the salad quantity chopped by Tammy is what percent greater than the quantity chopped by Tom?

A. 44%
B. 100%
C. 125%
D. 225%
E. 400%

The OA is C.

I'm confused with this PS question. Experts, any suggestion about how can I solve it?

Can I take an specific time? like 6 minutes for example,

in 6 minutes Tom chops 4lb
in 6 minutes Tammy chops 9 lb

Then I can say that in the same period of time, Tammy chopped 70% of the total and Tom chopped 30%. Now, how can I get the correct answer with this resul?

Thanks in advance.

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Source: Beat The GMAT — Problem Solving | Fri Jan 19, 2018 6:50 am

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ErikaPrepScholar: Legendary Member; Posts: 503; Joined: Thu Jul 20, 2017 9:03 amFollowed by: 15 members; Thanked: 86 times; GMAT Score:770

by ErikaPrepScholar » Fri Jan 19, 2018 7:43 am

I'm confused with this PS question. Experts, any suggestion about how can I solve it?

Can I take an specific time? like 6 minutes for example,

in 6 minutes Tom chops 4lb
in 6 minutes Tammy chops 9 lb

You're almost there with this method! We want to find how many percent greater the amount Tammy chopped is than the amount Tom chopped. Tammy chopped 9 - 4 = 5lbs more than Tom. Tom chopped 4lbs in total. So to find the percent greater, we take 5/4 *100 = 125%. So 4lbs plus 125% of 4lbs gives 4lbs plus 5lbs, which is 9lbs. So the amount Tammy chopped is 125% greater than the amount Tom chopped.

Because Tom and Tammy will continue chopping at the same rate all the way up to 65lbs of salad, the difference in the amount of salad chopped between them will change, but the percent difference will not. So the answer is C!

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by [email protected] » Fri Jan 19, 2018 7:03 pm

Hi LUANDATO,

We're told that when Tom works alone he chops 2 pounds of salad in 3 minutes and when Tammy works alone she chops 3 pounds of salad in 2 minutes. They start working at the same time and chop 65 pounds of salad. Of those 65 lb., we're asked what percent greater is the amount chopped by Tammy than the quantity chopped by Tom.

Since both Tammy and Tom chop at a constant rate - and chop for the same amount of time - the fact that they chopped a total of 65 pounds is actually irrelevant. Here's why:

In 6 minutes...
Tom chops 4 pounds
Tammy chops 9 pounds

Tammy will always chop 5 MORE pounds than Tom every 6 minutes. Using the Percent Change formula, that means Tammy chops...

Percent Change = (New - Old) / (Old) = (9 - 4) / 4 = 5/4 = 1.25 = 125% more than Tom

If you did the extra work to include he 65 total pounds, then you would get the same answer:

In 30 minutes...
Tom chops 20 pounds
Tammy chops 45 pounds

Percent Change = (New - Old) / (Old) = (45 - 20) / 20 = 25/20 = 5/4 1.25 = 125% more than Tom

Final Answer: C

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Rich

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8137; Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members; Location: Los Angeles, CA; Thanked: 43 times

by Scott@TargetTestPrep » Sun Jan 21, 2018 6:14 pm

LUANDATO wrote:When Tom works alone he chops 2 lb. salad in 3 minutes, and when tammy works alone she chops 3 lb. salad in 2 minutes. They start working together, and after some time finish chopping 65 lb. of salad. Of those 65 lb., the salad quantity chopped by Tammy is what percent greater than the quantity chopped by Tom?

A. 44%
B. 100%
C. 125%
D. 225%
E. 400%

We use the "percent greater than" formula: (Tammy's rate - Tom's rate)/Tom's rate x 100%.

Since Tom's rate is 2/3 and Tammy's rate is 3/2, when they work together, Tammy's work will always be:

(3/2 - 2/3)/2/3 x 100

(9/6 - 4/6)/2/3 x 100

(5/6)/(2/3) x 100 = 5/6 x 3/2 x 100 = 15/12 x 100 = 5/4 x 100 = 125% greater than Tom's.

Answer: C

Scott Woodbury-Stewart
Founder and CEO
[email protected]

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