In kickboxing, it is found that the force, f, needed to break a board, varies inversely with the length, l, of the board. if it takes 7 pounds of pressure to break a board that is 3 feet long, how long is a board that requires 5 pounds of pressure to break?

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-21 or 4

Step-by-step explanation:

Step-by-step explanation:

Let the smaller number be y and the larger number be x , then

x - y = 8 equation 1

From the second statement

equation 2

combining the two equations:

equation 1

  equation 2

solving the system of equation by substitution method , from equation 1 , make y the subject of the formula.

equation 3

substitute equation 3 into equation 2 , we have

Factorizing the quadratic expression , we have

That is

or

When   ,

                   (-13 , -21 )

when  ,

                      ( 12 ,4 )

Check:

-13 - (-21)

-13 + 21 = 8

Also

12 - 4 = 8

Therefore , the smaller number is -21 or 4

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step-by-step explanation:

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