Can anyone solve this little problem?

Sam Bede · Joined: 05 Aug 2007 Posts: 2

Hi

Sorry to be a dunce, but I'm sure some maths whiz can solve this.

I'd really appreciate your help.

I have a value, call it X. And I know it's risen over the year by a
percentage, say Y.

How do I calculate what the original value of X is?

My attempts have been missing the mark. Your help would be greatly
appreciated.

Thanks so much.
Sam

Archived from group: uk>education>maths

Dan Wood · Joined: 05 Aug 2007 Posts: 4

Sam Bede wrote:
> Hi
>
> Sorry to be a dunce, but I'm sure some maths whiz can solve this.
>
> I'd really appreciate your help.
>
> I have a value, call it X. And I know it's risen over the year by a
> percentage, say Y.
>
> How do I calculate what the original value of X is?
>
> My attempts have been missing the mark. Your help would be greatly
> appreciated.
>
> Thanks so much.
> Sam
>
>
>

Lots of ways to do this. Perhaps the easiest for you to think about
would be to imagine your original X is '100 percent'.

So when it rises by Y, you end up with '100 and Y percent'

So, to go backwards, DIVIDE your new amount by '100 and Y' to find one
percent, and then multiply by 100...

Hope that makes sense!

Dan.

~Bitzchick~ · Joined: 05 Aug 2007 Posts: 18

Sam Bede wrote:
> Hi
>
> Sorry to be a dunce, but I'm sure some maths whiz can solve this.
>
> I'd really appreciate your help.
>
> I have a value, call it X. And I know it's risen over the year by a
> percentage, say Y.
>
> How do I calculate what the original value of X is?
>
> My attempts have been missing the mark. Your help would be greatly
> appreciated.
>
> Thanks so much.
> Sam

X = original amount
X/100 = percentage of X

Y is new value of X after it has risen by X/100

So

New amount X has risen by X+ X/100 = Y

Factorising:

X(1+0.01) = Y

X (1.01) =Y

Therefore X = Y/1.01

sheri

Stan Brown · Joined: 05 Aug 2007 Posts: 233

Sat, 21 Apr 2007 09:30:46 GMT from Sam Bede spam.com>:
> I have a value, call it X. And I know it's risen over the year by a
> percentage, say Y.
>
> How do I calculate what the original value of X is?

If something rises by 15%, its new value is 1 + 15% of its old value.
15% = 15/100, so the new value is (1 + 15/100) times the old value,
or (1 + 0.15) times the old value, or 1.15 times the old value.

Your value rose by Y%, so the new value is (1 + Y/100) times the old
value Let's call the old value V. Then you have
(1 + Y/100) * V = X
You know X and Y and you want to know V.

Divide:
V = X / (1 + 100/Y)

Now plug and chug. Example: X = 1100 pounds, Y = 20%. Then
1 + 100/Y = 1.20
V = 1100 pounds / 1.20 = about 916.67 pounds

Check: 20% of 916.67 is 183.33. Adding the amount of increase to the
original gives 916.67+183.33 = 1100.00.

--
Stan Brown, Oak Road Systems, Tompkins County, New York, USA
http://OakRoadSystems.com/

Sam Bede · Joined: 05 Aug 2007 Posts: 2

THANKS for helping with this.

I couldn't work it out and appreciate your kind assistance.

Sam..

"Sam Bede" wrote in message $M.8954@news-server.bigpond.net.au...
> Hi
>
> Sorry to be a dunce, but I'm sure some maths whiz can solve this.
>
> I'd really appreciate your help.
>
> I have a value, call it X. And I know it's risen over the year by a
> percentage, say Y.
>
> How do I calculate what the original value of X is?
>
> My attempts have been missing the mark. Your help would be greatly
> appreciated.
>
> Thanks so much.
> Sam
>
>
>

CWatters · Joined: 05 Aug 2007 Posts: 6

"Sam Bede" wrote in message$M.11258@news-server.bigpond.net.au...
> THANKS for helping with this.
>
> I couldn't work it out and appreciate your kind assistance.
>
> Sam..

As my teachers would say...

as an exercise now try working out the original sum if you have £X at the
end of TWO years growth at Y% per year compounded.

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