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10)    Joint variation might be a new one to you, NSS

We have this

A  = kds^2      

Where A is the amount of oil used, d is the distance  and s is the speed

As in other types of variation, we need to find the proportionality constant, k

So  we know that

30  =  k (85) (42)^2         divide both sides by  (85)(42)^2

30 / [ (85)(42)^2 ]  = k    1 / 4998

So we want to find A for this

A  =  (1 / 4998) (26) (54)^2   =    15.2  barrels

11.  Notice NSS,  that taking the product of the number of volunteers with their associated time in minutes, we have that

2 * 220  =  440

5 * 88  =  440

8 * 55 +  440

11*40 + 440

So....it appears that

nt  =  440