pizzas to bake

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sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 amFollowed by: 80 members; Location: India; Thanked: 267 times; GMAT Score:760

by sanju09 » Fri Jan 28, 2011 6:12 am

Tony has an order of 14 pizzas to bake. He baked an average of 8 pizzas per hour for the first 8 pizzas, and then he baked an average of 12 pizzas per hour for the remaining pizzas in the order. Assuming that he baked the full order, and only that order, without stopping to take any breaks, how many pizzas did Tony bake per hour, on average?
(A) 9
(B) 9 1/3
(C) 9 2/3
(D) 10
(E) 10 1/3

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Source: Beat The GMAT — Problem Solving | Fri Jan 28, 2011 6:12 am

jaxis: Master | Next Rank: 500 Posts; Posts: 101; Joined: Sun Sep 26, 2010 9:33 am; Thanked: 5 times

by jaxis » Fri Jan 28, 2011 6:17 am

sanju09 wrote:Tony has an order of 14 pizzas to bake. He baked an average of 8 pizzas per hour for the first 8 pizzas, and then he baked an average of 12 pizzas per hour for the remaining pizzas in the order. Assuming that he baked the full order, and only that order, without stopping to take any breaks, how many pizzas did Tony bake per hour, on average?
(A) 9
(B) 9 1/3
(C) 9 2/3
(D) 10
(E) 10 1/3

9 1/3

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aleph777: Master | Next Rank: 500 Posts; Posts: 131; Joined: Fri Jun 18, 2010 10:19 am; Location: New York, NY; Thanked: 10 times

by aleph777 » Fri Jan 28, 2011 6:22 am

We know that the total he has to bake is 14, and we're looking for his overall average rate. That means we need to know how many pies he baked in total and the total time he spent baking them. Then it's a simple R=W/T problem.

Start with the first part of the statement.

Tony baked an average of 8/hr for the first 8 pizzas. So how long did it take him to bake those 8 pizzas? T=W/R, so T=8/8=1 hour.

The next part of the statement says he baked at a rate of 12/hour until he finished the order. We know the order is 14, but he's already baked 8, so that means he has 6 more pies to bake. Again, we need to solve for his time at this rate. So 6/12 = 1/2 hour.

Now we can sum his times and sum the total number of pies to find his overall average rate.

Total time = 1 + 1/2 = 3/2
Total pies = 14.

And to solve for total Rate, we again use the rate formula: R=W/T. 14/(3/2) = 14*2/3 = 28/3 = 9 1/3.

Answer B

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arora007: Community Manager; Posts: 1048; Joined: Mon Aug 17, 2009 3:26 amFollowed by: 27 members; Location: India; Thanked: 51 times; GMAT Score:670

by arora007 » Fri Jan 28, 2011 6:33 am

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