how do i calculate 67% of an amount, only knowing the 67% result?

[lassard]

For example, I can receive 30 ebony by trading away 20 dye. But if I only have 18 dye, how do I calculate how much ebony I can get?

I end up trying all numbers, dividing 18 into 26, 27, 28 to find the exact amount (which was 27). I need a more efficient way.

This isn't a math problem - it's for a game. Based on math needed pre-algebra seemed best forum. Please move thread if needed, thank you.

 

[Deleted member 4993]

For example, I can receive 30 ebony by trading away 20 dye. But if I only have 18 dye, how do I calculate how much ebony I can get?

I end up trying all numbers, dividing 18 into 26, 27, 28 to find the exact amount (which was 27). I need a more efficient way.

This isn't a math problem - it's for a game. Based on math needed pre-algebra seemed best forum. Please move thread if needed, thank you.

Hint:

Assume that:

the number of of Ebony = E

the number of of Dye = D

Then

E/D = 30/20 = 3/2

When D = 18

E/18 = 3/2 → E = 3/2 * 18 = 27

 

[Dr.Peterson]

For example, I can receive 30 ebony by trading away 20 dye. But if I only have 18 dye, how do I calculate how much ebony I can get?

I end up trying all numbers, dividing 18 into 26, 27, 28 to find the exact amount (which was 27). I need a more efficient way.

This isn't a math problem - it's for a game. Based on math needed pre-algebra seemed best forum. Please move thread if needed, thank you.

To solve this without using algebra at all, note that you have 18/20 of the amount of dye needed for 30 ebony, so you can get 18/20 * 30 ebony. Just do the fraction multiplication; it simplifies to 18*3/2 and then to 9*3 = 27.

Of course, the result could have been a non-whole number, in which case you presumably would have had to trade only part.