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The average (arithmetic mean) of the weight of 10 vehicles

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The average (arithmetic mean) of the weight of 10 vehicles [#permalink] New post 23 Apr 2012, 04:19
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Question Stats:

92% (02:14) correct 8% (00:41) wrong based on 38 sessions
The average (arithmetic mean) of the weight of 10 vehicles is 12 tons. The average weight of the group of vehicles increased by 2.4 tons after a new heavy duty truck was added to the group? What is the weight of the heavy duty truck?

A. 35 tons
B. 38.4 tons
C. 40.2 tons
D. 41.2 tons
E. 42 tons

Could one please render a good explanation.
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Re: The average (arithmetic mean) of the weight of 10 vehicles [#permalink] New post 23 Apr 2012, 04:40
Expert's post
dzodzo85 wrote:
The average (arithmetic mean) of the weight of 10 vehicles is 12 tons. The average weight of the group of vehicles increased by 2.4 tons after a new heavy duty truck was added to the group? What is the weight of the heavy duty truck?

A. 35 tons
B. 38.4 tons
C. 40.2 tons
D. 41.2 tons
E. 42 tons

Could one please render a good explanation.


The sum of the weights of 10 vehicles is 10*12=120 tons. Say the weight of 11th vehicle is x tons, then the new average, which is now 12+2.4=14.4 equal, to new \ average=\frac{new \ total \ weight}{new \ # \ of \ vehicles} --> 14.4=\frac{120+x}{11} --> x=38.4.

Answer: B.
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Re: The average (arithmetic mean) of the weight of 10 vehicles   [#permalink] 23 Apr 2012, 04:40
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