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**ganesh****Moderator**- Registered: 2005-06-28
- Posts: 20,930

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.

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

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

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**darthradius****Member**- Registered: 2005-11-28
- Posts: 97

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

-Bertrand Russell

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**ganesh****Moderator**- Registered: 2005-06-28
- Posts: 20,930

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

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

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**thinkdesigns****Member**- Registered: 2005-07-21
- Posts: 23

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

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**ganesh****Moderator**- Registered: 2005-06-28
- Posts: 20,930

**Well done, thinkdesigns! **

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

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

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**JaneFairfax****Member**- Registered: 2007-02-23
- Posts: 6,868

**A # 2**

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**JaneFairfax****Member**- Registered: 2007-02-23
- Posts: 6,868

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**keveenjones****Member**- Registered: 2010-04-18
- Posts: 2

The weight of person A is 72.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 104,339

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.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **A number by itself is useful, but it is far more useful to know how accurate or certain that number is.**

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**jonnyj99****Member**- Registered: 2010-08-16
- Posts: 4

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),

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**ganesh****Moderator**- Registered: 2005-06-28
- Posts: 20,930

Hi jonnyj99,

The posts are understood better with LaTeX.

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

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 104,339

Hi jonnyj99;

Welcome to the forum!

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

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **A number by itself is useful, but it is far more useful to know how accurate or certain that number is.**

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**G-man****Member**- Registered: 2011-02-28
- Posts: 16

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

Maths!......

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 104,339

Hi G-man;

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

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **A number by itself is useful, but it is far more useful to know how accurate or certain that number is.**

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