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 hello_math September 18th, 2016 07:17 AM

formula for direct or inverse related values

Hello All

via the following x, y values , a formula needs to be decided for the 'Y ' variable.

Basicaaly Consider the table below for x and y (are they directly proportional or are they inversely related ? ). and also to find out the corresponding formula. Pl. see the image

http://s6.postimg.org/nph5u40dd/math.png

I have seemed to find the answer BUT with trial and error :p
for e.g ( 4,11 :--> 4 X 2 = 8 +3) say this is 'Try 1'

for ( 12,31 :---> 12 X 2 = 24 +7) and so on

also in the (8+3) above , take the '3' & in (24+7) above take the '7' , which gives a pattern of 'multiply with 2' +1 (notice the '1')

and when I would repeat the above once again but this time with
for e.g ( 4,11 :---> 4 X 3 = 12) say this is 'Try 2'

then I just take the (a gamble) of 'Try 1' and 'Try 2' and can settle for 2.5 as the factor :)

so y = 2.5x + 1 is the formula ;)

but is there a 'proper' way to get the formula( other than guesswork and a not structural method like I have done above) ?