# SOLUTION: Direct and Indirect Variation. I do not understand how to solve this or any problems such as these. y varies directly with x. y =15 when x=4. what is the value of y when x=5

Algebra ->  Algebra  -> Average -> SOLUTION: Direct and Indirect Variation. I do not understand how to solve this or any problems such as these. y varies directly with x. y =15 when x=4. what is the value of y when x=5       Log On

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 Question 618635: Direct and Indirect Variation. I do not understand how to solve this or any problems such as these. y varies directly with x. y =15 when x=4. what is the value of y when x=5 or y varies inversely with x y=8 when x=8. what is the value of y when x=4 Found 3 solutions by richwmiller, nerdybill, MathTherapy:Answer by richwmiller(9135)   (Show Source): You can put this solution on YOUR website!direct y=kx 15=k4 15/4=k y=5*15/4 y=75/4 indirect y=x/k 8=8/k k=1 y=x/1 y=5/1 y=5 Answer by nerdybill(6958)   (Show Source): You can put this solution on YOUR website!y varies directly with x. y =15 when x=4. what is the value of y when x=5 . When you see "y varies directly with x" think: y = kx (where k is a constant) find this constant by plugging in "y =15 when x=4" from the problem: 15 = k(4) 15/4 = k . Now, our equation is: y = (15/4)X We can now answer: what is the value of y when x=5 y = (15/4)X y = (15/4)5 y = 75/4 y = 18.75 . y varies inversely with x y=8 when x=8. what is the value of y when x=4 When you see "y varies inversely with x" think: y = k/x (where k is a constant) find this constant by plugging in "y=8 when x=8" from the problem: 8 = k/8 8/8 = k 1 = k . Now our equation is: y = 1/x We can now answer: what is the value of y when x=4 y = 1/x y = 1/4 y = .25 Answer by MathTherapy(1424)   (Show Source): You can put this solution on YOUR website!Direct and Indirect Variation. I do not understand how to solve this or any problems such as these. y varies directly with x. y =15 when x=4. what is the value of y when x=5 or y varies inversely with x y=8 when x=8. what is the value of y when x=4 Direct y = kx ----- Substituting 15 for y, and 4 for x 4k = 15 k (constant of variation) = y = kx ----- Substituting for k, and 5 for x , or Inverse or Indirect y = k/x ----- Substituting 8 for y, and 8 for x k (constant of variation) = y = k/x ----- Substituting 64 for k, and 4 for x Send comments and “thank-yous” to “D” at MathMadEzy@aol.com