# Thread: Formula

1. ## Formula

hello,

i have the following formules:

a = ?
b = (a + 650 * 2a/5.5) + (a * 450)
c = (b / 4) - 270

when i enter a = 30, c will be 10238.

now i need a formula where i can enter d = 10238, and it calculates f = 30.

I'm really confused, i hope somebody can help me.

Thanks
~ Frank

2. ## More information please

Hello Frank

Welcome to Math Help Forum!
Originally Posted by frank9999
hello,

i have the following formules:

a = ?
b = (a + 650 * 2a/5.5) + (a * 450)
c = (b / 4) - 270

when i enter a = 30, c will be 10238.

now i need a formula where i can enter d = 10238, and it calculates f = 30.

I'm really confused, i hope somebody can help me.

Thanks
~ Frank
I think you will need to clarify this question if you want a helpful answer. You have mentioned $\displaystyle a, b$ and $\displaystyle c$, and then you ask for a formula that gives the value $\displaystyle f = 30$, when $\displaystyle d = 10238$.

This doesn't really make a lot of sense. Could you give us some more information please?

Grandad

3. ## Better explaination

ok ill try to explain it again,

i have the following formules:

when i enter a = 30 in the formule above, it will return c = 10238.

now i need a formula where i can input any type of C value, and it will return the corresponding a value according to the formula used above.

For example i put in c = 10238, it will return a = 30.

Thanks
~ Frank

4. Hello Frank
Originally Posted by frank9999
ok ill try to explain it again,

i have the following formules:

when i enter a = 30 in the formule above, it will return c = 10238.

now i need a formula where i can input any type of C value, and it will return the corresponding a value according to the formula used above.

For example i put in c = 10238, it will return a = 30.

Thanks
~ Frank
I understand now what you require - you simply need the inverse formula. However, I do not understand how the formula you have quoted gives $\displaystyle c = 10238$ when $\displaystyle a = 30$.

You have:
$\displaystyle b = (a + 650 \times 2\tfrac{a}{5.5}) + (a\times450)$
The part that is unusual is $\displaystyle 2\tfrac{a}{5.5}$. This really means $\displaystyle 2+\tfrac{a}{5.5}$. So when $\displaystyle a = 30$:
$\displaystyle b = (30 + 650 \times (2+\tfrac{30}{5.5}))+(30\times 450)$
$\displaystyle = 18375.45...$
and this then gives:
$\displaystyle c = 4323.86...$
Please clarify what you mean by $\displaystyle 2\tfrac{a}{5.5}$. Once you have done this, we may be able to reverse the formula to get $\displaystyle a$ in terms of $\displaystyle c$.

Grandad

5. Originally Posted by Grandad
Hello FrankI understand now what you require - you simply need the inverse formula. However, I do not understand how the formula you have quoted gives $\displaystyle c = 10238$ when $\displaystyle a = 30$.

You have:
$\displaystyle b = (a + 650 \times 2\tfrac{a}{5.5}) + (a\times450)$
The part that is unusual is $\displaystyle 2\tfrac{a}{5.5}$. This really means $\displaystyle 2+\tfrac{a}{5.5}$. So when $\displaystyle a = 30$:
$\displaystyle b = (30 + 650 \times (2+\tfrac{30}{5.5}))+(30\times 450)$
$\displaystyle = 18375.45...$
and this then gives:
$\displaystyle c = 4323.86...$
Please clarify what you mean by $\displaystyle 2\tfrac{a}{5.5}$. Once you have done this, we may be able to reverse the formula to get $\displaystyle a$ in terms of $\displaystyle c$.

Grandad
It didn't mean 2 + (a/5.5), i wanted to say 2^(a/5.5) (to the power of) or however you say that in english:P

so 2^(a/5.5) = 2^(30/5.5) = 2^5.5 = 45

b = (30 + 650 * 45) + (30 * 450) = 42780

c = 10425, depends on how you round some numers.

hope that helped a bit.

6. Hello Frank
Originally Posted by frank9999
It didn't mean 2 + (a/5.5), i wanted to say 2^(a/5.5) (to the power of) or however you say that in english:P

so 2^(a/5.5) = 2^(30/5.5) = 2^5.5 = 45

b = (30 + 650 * 45) + (30 * 450) = 42780

c = 10425, depends on how you round some numers.

hope that helped a bit.
I see. In that case, it is impossible to find a formula which will enable you to work backwards. The only thing I can suggest is that you set up these equations in a spreadsheet (e.g. Excel) and then use a Goal Seek tool to give you the answer.

Grandad