# Find third value

I have a very simple problem but I feel like I am brain-dead.

I cant figure it out how to calculate this in Java:

1321 = 0
1771 = 640
1500 = ?


Thanks.

Edit: Sorry for no context. (And english not my first language) I must basically calculate the value that number 1500 represents. If 1321 is min (=0) and 1771 is max (=640) where does 1500 fall in (between 0 and 640) ?

I hope I am more clear now :)

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– joriki Jul 10 '12 at 10:38
Um, what? ${}{}$ – anon Jul 10 '12 at 10:48
Some context would be very helpful. $1321$ is almost never $0$, and when it is, $1721$ isn't usually $640$. Are you working with modular arithmetic? – Cameron Buie Jul 10 '12 at 10:50
I updated my question. I hope I am more clear. – mrkok Jul 10 '12 at 10:58
Looks like the question is about linear interpolation between data points $(1321,0)$ and $(1771,640)$, in particular about how to find $y$ such that $(1500,y)$ would be on the same line. The answer comes from the equation of the line passing through two known points. Have you seen that in school algebra? – Jyrki Lahtonen Jul 10 '12 at 11:04

linear interpolation?

scale x ranges from 1321 to 1771 scale y you want to range from 0 to 640

gradient = (640 - 0) / (1771 -1321)

1500 -1321 = gradient ( x - 0)

i think it is $385$ – dato datuashvili Jul 10 '12 at 11:22
i dont know exactly if it is way to solve this problem,but i think about one thing,if $1321=0$ and $1771=640$ then for calculating where does fall $1500$,we have to consider what is the difference from min to $1500$ and from $1500$ to max value and make proportion. if we do so we get $450/179=640/x$ from this $x=254$,i think that we could solve this problem like this way