Math Is Fun Forum
  Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ -¹ ² ³ °

You are not logged in.

#1 2006-03-10 16:35:17

ganesh
Moderator
Registered: 2005-06-28
Posts: 21,319

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.


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.

Offline

#2 2006-03-10 18:24:00

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

Re: Average


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

Offline

#3 2006-03-10 18:36:14

ganesh
Moderator
Registered: 2005-06-28
Posts: 21,319

Re: Average

CM2_VeryGood.jpg


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.

Offline

#4 2006-04-21 07:13:52

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

Offline

#5 2006-04-21 16:28:34

ganesh
Moderator
Registered: 2005-06-28
Posts: 21,319

Re: Average

Well done, thinkdesigns! smile


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.

Offline

#6 2009-01-04 12:24:46

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

Re: Average

A # 2

Offline

#7 2009-02-06 23:39:05

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

Re: Average

Offline

#8 2010-04-18 19:15:38

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

Re: Average

The weight of person A is 72.

Offline

#9 2010-04-18 19:49:38

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 105,288

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.


In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
No great discovery was ever made without a bold guess.

Offline

#10 2010-08-16 16:18:46

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),

Offline

#11 2010-08-16 21:18:38

ganesh
Moderator
Registered: 2005-06-28
Posts: 21,319

Re: Average

Hi jonnyj99,

The posts are understood better with LaTeX.


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.

Offline

#12 2010-08-16 21:36:14

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 105,288

Re: Average

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.
No great discovery was ever made without a bold guess.

Offline

#13 2011-02-28 17:34:15

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

Re: Average

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


Maths!......sleep

Offline

#14 2011-02-28 21:12:39

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 105,288

Re: Average

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.
No great discovery was ever made without a bold guess.

Offline

Board footer

Powered by FluxBB