Help with formula

[Kelvin]

Hi There,
Can anyone help me. I need to solve x=y(0.2y) in terms of y. Practically I need to find, for a given amount, how much is cost and how much is VAT at 20%. For example, if I want to charge a total of say £20 for an item, how much is it before VAT is added.
Thanks.

[Prudie]

If your total is £20 incl VAT at 20% then to find the pre-VAT price divide by 120 and multiply by 100
20/120 X 100 =approx £16.67

[Kelvin]

Thanks very much Prudie, I was trying to enter the formula in a spreadsheet and had a mental block!

[mike11111]

Prudie is correct but I don't think that the answer is arrived at by the formula you give. My maths is very rusty (O Level 1964) but I read it as:
x = y(0.2y)
= x = y²/5
= y² = 5x
= y = √5x.

[Prudie]

You're right Mike. Kelvin's formula should be x =y +0.2y (where x is the £20)

[mibn2cweus]

. . . so then y = x - 0.2 y . . . right?

[THECORBYLOON]

If it's in a spreadsheet

GROSS in A1 and the figure in B1
NET in A2 B2=A1*100/120
VAT in A3 B3=B2*0.2

[rov1100]

I make Prudie's answer correct. Mathematicians usually double check their answers.

ie £16.67 @ 20% VAT = £20

[annieigma]

Hi,
I am glad I went to this part of the answer bank, I really thought most of the people on here were like me, a bit thick, but well done, I really feel confident about asking qustions now.
annie.

[ChuckFickens]

Not sure why you'd be worried about asking questions, anne... nobody know everything.

but the above answers seem a little long winded... just divide by 1.2 to find a VAT amount.

I.E.

20 / 1.2 = 16.67 is the amount without VAT.

then

20 - 16.67 = 3.33 is the amount of vat.

[Maydup]

That's what I'd do chuck.......

divide by 1.2 to take VAT off or multiply by 1.2 to add it on.

[ladyalex]

and I doubt you'd find many people were 'thick'

[ChuckFickens]

Precisely, maidup.

People complicate it too much.

And for those interested.. with the old 17.5% vat it would be

20 / 1.175 = 17.02 without vat

so

20 - 17.02 = 2.88

Percentages are easy to work out because the translate exactly into decimals.

[Prudie]

Most of these 'complicated' answers revolved around Kelvin's incorrect x,y equation.
Lots of people do not find percentages easy to work out.

[Old_Geezer]

Whatever gave you the impression that people on here were a bit thick ? That's supposed to be a secret !