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Re: The average weight of a group of 30 friends increases by 1 kg when the [#permalink]
Bunuel wrote:
The average weight of a group of 30 friends increases by 1 kg when the weight of their football coach was added. If average weight of the group after including the weight of the football coach is 31 kg, what is the weight of their football coach?

A. 31 kg
B. 60 kg
C. 61 kg
D. 62 kg
E. 91 kg

Weight of the coach is 31*31-30*30 = 61
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The average weight of a group of 30 friends increases by 1 kg when the [#permalink]
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Here is my approach to this one ->

sum(30)=900
sum(31)=961

Hence Coach must be 61 pounds

Hence C
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Re: The average weight of a group of 30 friends increases by 1 kg when the [#permalink]
Bunuel wrote:
The average weight of a group of 30 friends increases by 1 kg when the weight of their football coach was added. If average weight of the group after including the weight of the football coach is 31 kg, what is the weight of their football coach?

A. 31 kg
B. 60 kg
C. 61 kg
D. 62 kg
E. 91 kg

31*31 * 30*(31 - 1 ) = Weight of football coach

Weight of football coach = 961 - 900

So, Weight of football coach = 61

Hence correct answer will be C. 61 kg
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Re: The average weight of a group of 30 friends increases by 1 kg when the [#permalink]
Y/30=30

(C+Y)/31=31

C+Y-Y=31^2-30^2=(31-30)(31+30)=1*61
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Re: The average weight of a group of 30 friends increases by 1 kg when the [#permalink]
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