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# Maths question

## Sure I used to know how to do this!

#### goingincircles

12:41 pm on Dec 1, 2006 (gmt 0)

#### Junior Member

joined:June 27, 2005
posts:59
votes: 0

I have a number, and I know this number is 70% of a higher number, but I don't know the higher number. How do I work out what the higher number was?

e.g. if my number is 70, then the higher number would be 100. Any ideas on how to work this out?

#### goingincircles

12:44 pm on Dec 1, 2006 (gmt 0)

#### Junior Member

joined:June 27, 2005
posts:59
votes: 0

Hmmm.. just been fiddling about on a calculator.

x = the number you know

x * (((100 - x) / x) + 1)

seems to do it. I think.

#### jecasc

12:47 pm on Dec 1, 2006 (gmt 0)

#### Senior Member from DE

joined:May 8, 2003
posts:1144
votes: 3

I think it should be

x / 70 * 100

#### goingincircles

12:47 pm on Dec 1, 2006 (gmt 0)

#### Junior Member

joined:June 27, 2005
posts:59
votes: 0

ha ha - or not

#### AWildman

12:47 pm on Dec 1, 2006 (gmt 0)

#### Preferred Member

joined:Apr 22, 2003
posts:441
votes: 0

So, taking your example of 70,

70=.7x
70/.7 = x
100 = x

The trick I learned was to form a question.

"70 is 70% of what number?"

The "is" refers to an "="
The "of" refers to multiplication.
The "what" is an unknown variable.

That is the only way I remember after all these years!

Conversely,
"70% of 100 is what?"
.7 X 100 = n

Okay, its a dumb trick, but it works for me.

#### goingincircles

12:48 pm on Dec 1, 2006 (gmt 0)

#### Junior Member

joined:June 27, 2005
posts:59
votes: 0

That was a reply to my thread by the way, not yours!

#### goingincircles

12:49 pm on Dec 1, 2006 (gmt 0)

#### Junior Member

joined:June 27, 2005
posts:59
votes: 0

Thanks all! Was working late last night and my brain isn't functioning quite as it should be.

#### BillyS

4:17 pm on Dec 1, 2006 (gmt 0)

#### Senior Member

joined:June 1, 2004
posts:3181
votes: 0

Just write the equation as you think through it...

What Number (N) when multiplied by 70% equals 70?

N x 0.7 = 70
N = 70/0.7
N = 100