Find an equation of combined variation where a varies directly as b and inversely as c. One set of values is a = 4, b = 12, and c = 9. Find a when b = 7 and c = 3.

Combined equation is  

Step-by-step explanation:

a varies directly as b and  inversely as c.

This can be written as

a =

a =  kb

where k is the proportionality constant

-------------------------------------(1)

Now lets find the k value bu substituting the given a, b,c values

36 =  12 k

k = 3

Thus the eq(1) becomes

Let us now find the value of a  when b=7  and c = 3

a = 7

on monday rodney ate 1/4th of the sandwich = 3/12

on tuesday he ate 1/3rd of the sandwich = 4/12

therefore in total he has eaten = 3/12 + 4/12 = 7/12

thus we can say that he has eaten 7/12 of the sandwich on monday and tuesday alltogether.

happy to

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there are infinitely many solutions.