Question 610628
I think the question should be phrased as:
"What is the average speed of the 2nd vehicle in order to catch the 1st?"
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The head start of the 1st vehicle is {{{ .5 }}} mi
Start a stop watch when the 2nd vehicle leaves
{{{ 1 }}} mi = the distance that the 2nd vehicle has
to travel until it catches the 1st one.
Let {{{ t }}} = the time in hours on the stopwatch from when
the 2nd vehicle leaves until it catches the 1st one. 
Let {{{ r }}} = the average speed of the 2nd vehicle
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Equation for 1st vehicle:
(1) {{{ 1 - .5 = 67t }}}
Equation for 2nd vehicle:
(2) {{{ 1 = r*t }}}
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(1) {{{ .5 = 67t }}}
(1) {{{ t = .5/67 }}}
(1) {{{ t = 1/134 }}}
(1) {{{ 1/t = 134 }}}
and
(2) {{{ 1 = r*t }}}
(2) {{{ r = 1/t }}}
(2) {{{ r = 134 }}}
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The average speed of the 2nd vehicle must be at least 134 mi/hr