Math Is Fun Forum

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 48,384

Average

A # 1

The average weight of three men A, B, and C is 84 kg. A fourth man D joins them and the average weight of the four becomes 80 kg. If E whose weight is 3 kg more than D replaces A, then the average weight of B, C, D, and E becomes 79 kg. Find the weight of A.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

darthradius

Member

Registered: 2005-11-28

Posts: 97

Re: Average

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The greatest challenge to any thinker is stating the problem in a way that will allow a solution.
                                                             -Bertrand Russell

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 48,384

Re: Average

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

thinkdesigns

Member

Registered: 2005-07-21

Posts: 23

Re: Average

Not sure but
A+B+c=252 ( average of 84*3) eq1
A+b+c+d=320 eq2
eq1 -eq2
d=68
b+c+d+e=316 eq3
e=d+3
sub into eq3
b+c+2d+3=316 eq4
eq2-eq4
A-d-3=4
a=d+7
(knowing d is 68)
a=75

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 48,384

Re: Average

Well done, thinkdesigns!

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

JaneFairfax

Member

Registered: 2007-02-23

Posts: 6,868

Re: Average

A # 2

JaneFairfax

Member

Registered: 2007-02-23

Posts: 6,868

Re: Average

keveenjones

Member

Registered: 2010-04-18

Posts: 2

Re: Average

The weight of person A is 72.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Average

Hi keveenjones;

Welcome to the forum!

You get 3 equations in 4 unknowns:

Clear out fractions:

Subtract 1 from 2 and you get:

D = 68. Now use that in 2 and 3:

Subtract 2 from 1

A = 75.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

jonnyj99

Member

Registered: 2010-08-16

Posts: 4

Re: Average

There are many different types of equation for find the average. I give the easy equation are given the below.

    y = f^{-1}\left(\frac{f(x_1)+f(x_2)+\cdots+f(x_n)}{n}\right),

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 48,384

Re: Average

Hi jonnyj99,

The posts are understood better with LaTeX.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Average

Hi jonnyj99;

Welcome to the forum!

Ganesh is right. You forgot the math tags on both ends of your latex.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

G-man

Member

Registered: 2011-02-28

Posts: 16

Re: Average

[hide=A's weight]85kg[hide/]

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Maths!......

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Average

Hi G-man;

That is close but the answer is 75, please see post #9.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.