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 2005-07-10 05:26:37

anonymous
Guest

proportions

3/(5x+1)=2/9, x=?

#2 2005-07-10 06:36:25

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

Re: proportions

3/(5x+1)=2/9
Multiply by (5x+1): 3=2(5x+1)/9
Multiply by 9: 27=2(5x+1)
Multiply out of brackets: 27=10x+2
Take away 2: 25=10x
Divide by 10: x=2.5

Hope this helps!


Why did the vector cross the road?
It wanted to be normal.

Offline

#3 2005-07-10 16:47:34

Jai Ganesh
Administrator
Registered: 2005-06-28
Posts: 45,956

Re: proportions

This can be explained in another way.
when you have a/b=c/d,
you get ad=bc.
In this problem,
3/(5x+1) = 2/9,
therefore, 9x3 = 2(5x+1)
27=10x+2
Move 2 to the other side, by changing the sign,
27-2 = 10x,
25=10x,
x = 25/10 = 2.5


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.

Offline

Board footer

Powered by FluxBB