Jointly Proportional

Definition of Jointly Proportional

If a variable z is jointly proportional to a set of variable x and y, the z = kxy, where k is the constant of proportionality.

More About Jointly Proportional

    Jointly proportional is also known as joint variation.

Example of Jointly Proportional

    The kinetic energy, E, of a moving object is jointly proportional to its mass, m, and the square of its speed, v.i.e., E = k .m. v2

Video Examples: Art of Problem Solving: Joint Proportion

Solved Example on Jointly Proportional

Ques: If x is jointly Proportional to y and z when x = 4, y = 8 and z = 9, then find the value of x when y = 2 and z = 18.

    A. 1
    B. 0
    C. 2
    D. 4
    Correct Answer: C


    Step 1: x a k. y. z [joint proportional]
    Step 2: x = k. y. z
    Step 3: 4 = k. 8. 9 [Substituting the values for x, y, z.]
    Step 4: k = 1/18[Simplify.]
    Step 5: Therefore, x =1/18. 2. 18 [Substituting the values for k, y and z in x = k. y. z]
    Step 6: So, x = 2 [Simplify.]

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