 Name: ___________________Date:___________________

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### Grade 8 - Mathematics Direct Proportion - I

 Two variables are in direct proportion to one another if they are always in the same ratio. If two variables x and y are vary in such a way that their ratio x/y is a constant(k). Then x and y are said to vary directly or in direct variation "k" is called the constant of variation. \ If variables x and y are directly then x/y = k or x=ky. This is denoted by xĄy. Example: yĄx, and constant of variation is 6. Find y, when x=3, find x, when y=24. Solution: Since yĄx, we have y = kx But k = 6 Ţ y = 6x If x = 3 Ţ y = 6*3 = 18 If y = 25 Ţ 25 = 3x Ţ x = 25/3. Example: If 4 bottles of milk cost \$2, how many bottles can you buy for \$8? Solution: You can write this in proportion as 4:2 :: x:8 or 4/2 = x/8 Cross multiplying we get 2x = 32 x = 16 Answer: 16 bottles Directions: Solve the following problems. Also write atleast 10 examples of your own. Name: ___________________Date:___________________