Proportionate to the maximum number

HI All,

I am preparing a recipe chart of a food Item; which has this masala item which gets consumed proportionately; lets say to make 10 portion of food item 1.3 kgs of masala will be used and to prepare 50 portion we need only 5 kg. so i just want to proportionately reduce the qty based on the no of portion prepared.

10kg = 1.3 kg
15kg = ?
20kg =?
25kg= ?
30kg= ?
35kg= ?
40kg=?
45kg= ?
50kg = 5 kg

Thanks in advance
Nasha1991

If I've understood you correctly you can use TREND or FORECAST.
In the attached are several solutions. Both of these functions like it better if the known x-values are in a contiguous range and the known y-values are in their contiguous range. That's the case in the section at cell A14.
eg.
=TREND($B$24:$B$25,$A$24:$A$25,A15,TRUE)
or
=FORECAST.LINEAR(A15,$B$24:$B$25,$A$24:$A$25)
(you can drop the .LINEAR if you have eralier versions of Excel)

However, to make it more like your layout where the known values are at the top and bottom, and you want values inbetween.This is the case in the section starting at cell A1.
eg.
=TREND(IF({1,0},$B$3,$B$11),IF({1,0},$A$3,$A$11),A4,TRUE)
or
=FORECAST.LINEAR(A4,IF({1,0},$C$3,$C$11),IF({1,0},$A$3,$A$11))

Thanks a ton.