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29 March, 12:34

Annette drives her car 120120 miles and has a mean of a certain speed. if the mean speed had been 3mph3⁢mph more, she could have traveled 128128 miles in the same length of time. what was her mean speed?

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  1. 29 March, 15:07
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    So Annette's speed was 45 mph.

    Let's make 2 equations to represent Annette's speed.

    T*S = 120

    Where

    T = the time Annette has been driving.

    S = her mean speed.

    120 = number of miles she's traveled.

    and another equation that's

    T * (S+3) = 128

    So we now have 2 equations with 2 unknowns. They are

    T*S = 120

    T * (S+3) = 128

    Let's divide the top equation by S on both sides and the bottom equation by (S+3) on both sides giving

    T = 120/S

    T = 128 / (S+3)

    So we now know that 120/S is equal to 128 / (S+3). So let's make that equation and solve for S

    120/S = 128 / (S+3)

    Multiply both sides by S (S+3)

    120 (S+3) = 128S

    Distribute the 120 on the left

    120S + 360 = 128S

    Subtract 120S from both sides

    360 = 8S

    And divide both sides by 8

    45 = S

    So Annette's speed was 45 mph.
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