Variation and Proportion Indirect Proportion
The formula for indirect variation can be written as y=k/x where k is called the constant of variation. ***We can follow the same steps from direct variation!! The steps to follow to solve a problem with indirect variation: Write the equation: y = k/x Substitute for x and y Solve for k Rewrite the equation with k as the constant
Problem: Find an equation of indirect variation where y varies indirectly as x. One pair of values is y = 145 when x = Write the equation: y = k/xy = k/x Substitute for x and y145 = k/ Solve for k145(.8) = k, or k = Rewrite the equation with k y = 116/x as the constant
Problem: The time (t) required to do a certain job varies inversely as the number (n) of people working (assuming all work at the same rate). It takes 4 hours for 20 people to wash and wax the floors in a building. Find the equation of variation. y = time; x = number of people y = k/x = k/ = k, or k = 80 Equation: y = 80/x
Practice Problems: Answers 1. y = 25 when x = 3 Equation: y = 75/x 2. y = 45 when x = 2 Equation: y = 90/x 3. y = 80 when x =.7 Equation: y = 56/x 4. y =.8 when x = 4 Equation: y = 3.2/x
Practice Problems: Answers (Continued) 5. It takes 16 hours for 2 people to resurface a gym floor. How long would it take 6 people to do the job? Write the equation: y = k/xy = k/x Substitute for x and y16 = k/ Solve for k16(2) = k, or k = Rewrite the equation with k y = 32/x as the constant