Question #21560

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Answer 1 · 2017-09-15T11:44:36

Yes, you may let $n$ equal their original speed.

You will need the formula for speed to solve for $n$

$"speed"="distance"/"time"$

$rArr"distance"="speed"*"time"$

Let $n="initial speed"$

Then

$"final speed"=n-5$

The distance travelled to the destination is

$d_i=n*t=3.5n$

The distance travelled home is the same, but given by

$d_f=(n-5)t=4(n-5)$

Now equate the two expressions for distance and solve for n

$d_i=d_f$

$rArr3.5n=4(n-5)$

$rArr3.5n=4n-20$

$rArr0.5n=20$

$rArrn=40" "(mi)/h$