Question 995512
Let {{{ d }}} = the distance in miles 
Mary travels in time {{{ t }}} in hrs
{{{ d - 1.5 }}} = the distance in miles 
Janet travels in time {{{ t }}} in hrs
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Mary's equation:
(1) {{{ d = 7t }}}
Janet's equation:
(2) {{{ d - 1.5 = 5t }}}
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Substitute (1) into (2)
(2) {{{ 7t - 1.5 = 5t }}}
(2) {{{ 2t = 1.5 }}}
(2) {{{ t = .75 }}}
and
{{{ .75*60 = 45 }}}
In 45 min they will be 1.5 mi apart
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check:
(1) {{{ d = 7t }}}
(1) {{{ d = 7*.75 }}}
(1) {{{ d = 5.25 }}}
and
(2) {{{ d - 1.5 = 5t }}}
(2) {{{ d - 1.5 = 5*.75 }}}
(2) {{{ d - 1.5 = 3.75 }}}
(2) {{{ d = 5.25 }}}
OK