Question 334403: If r varies jointly as s and t, when r=90, s=8 and t=15. find r when s=7 and t=12.
Answer by Alan3354(69443)   (Show Source):
You can put this solution on YOUR website! If r varies jointly as s and t, when r=90, s=8 and t=15. find r when s=7 and t=12.
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You didn't specify, so I'll assume r varies directly, not inversely.
r = kst (k is some number)
Use the data given to find k
90 = k*8*15 = 120k
k = 90/120 = 3/4
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@ s=7, t=12
r = (3/4)*7*12
r = 63
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