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23 Apr 2012, 05:19
Kudos
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B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
5%
(low)
Question Stats:
96% (01:41) correct
4%
(01:38)
wrong
based on 138
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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.
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.
23 Apr 2012, 05:40
Kudos
Bookmarks
dzodzo85
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.
26 Dec 2014, 10:48
Kudos
Bookmarks
Hi All,
In these types of Weighted Average questions, you can always use the Average Formula (as Bunuel showed). There are often ways to solve the problem by doing "relationship math" - it's essentially the same math (but in a different order) and might save you some time if you're comfortable with the concepts involved.
Here, we know that the average of 10 vehicles is 12 tons. In real simple terms, we COULD say that we have 10 vehicles that weight 12 tons EACH. Adding another vehicle raises the AVERAGE WEIGHT of ALL the vehicles 2.4 tons. We're asked for the weight of this extra vehicle.
So, if we raise each of the 10 vehicles 2.4 tons, then each would weight 14.4 tons --> 10(+2.4 tons) = 24 extra tons
To keep the overall average at 14.4 tons, we have to include that weight in the extra vehicle too -->14.4 tons + the increase in the other vehicles.
This gives us 14.4 + 24 = 38.4 tons
Final Answer:
GMAT assassins aren't born, they're made,
Rich
In these types of Weighted Average questions, you can always use the Average Formula (as Bunuel showed). There are often ways to solve the problem by doing "relationship math" - it's essentially the same math (but in a different order) and might save you some time if you're comfortable with the concepts involved.
Here, we know that the average of 10 vehicles is 12 tons. In real simple terms, we COULD say that we have 10 vehicles that weight 12 tons EACH. Adding another vehicle raises the AVERAGE WEIGHT of ALL the vehicles 2.4 tons. We're asked for the weight of this extra vehicle.
So, if we raise each of the 10 vehicles 2.4 tons, then each would weight 14.4 tons --> 10(+2.4 tons) = 24 extra tons
To keep the overall average at 14.4 tons, we have to include that weight in the extra vehicle too -->14.4 tons + the increase in the other vehicles.
This gives us 14.4 + 24 = 38.4 tons
Final Answer:
GMAT assassins aren't born, they're made,
Rich
