How do you solve an indirect proportion problem in math?


To solve an indirect proportion math problem, identify the two given proportions. Next, multiply the increasing quantity and decreasing quantity of the known proportion to find the constant. Use the constant in the indirect proportion equation to solve for the unknown value.

  1. Identify the two proportions in the problem

    If given a problem asks how many hours it takes five people to paint a house if it previously took eight people 17 hours, determine which value increases when the other decreases. In this problem, when the number of people increases, the time decreases.

  2. Calculate the constant

    The formula to determine the constant is x * y = k. Since the time it takes to paint the house with five people is the unknown, time is assigned to the y variable, and the number of people is assigned to x. Therefore, the constant is 136.

  3. Calculate the unknown quantity

    The formula to solve an indirect proportion is y = (k / x). K is the constant, y is the unknown value and x is the known value. For example, if the constant is 136 and x equals five, the equation is (136 / 5) = 27.2. Therefore, painting the house takes 27.2 hours with five people.

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