Question 1031572
You can think of this as one of the cars standing
still and the other car moving at the sum of their speeds
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Let {{{ s }}} = the speed of the faster car in km/hr
{{{ s - 18 }}} = the speed of the slower car in km/hr
{{{ 3 }}} = time in hrs until they meet
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{{{ 540 = ( s + s - 18 )*3 }}}
{{{ 540 = 6s - 54 }}}
{{{ 6s = 594 }}}
{{{ s = 99 }}}
and
{{{ s - 18 = 81 }}}
The slower car's rate is 81 km/hr
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Check answer:
Let {{{ d[1] }}} = distance slower car travels in 3 hrs
Let {{{ d[2] }}} = distance faster car travels in 3 hrs
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(1) {{{ d[1] = 81*3 }}}
(1) {{{ d[1] = 243 }}} km
and
(2) {{{ d[2] = 99*3 }}}
(2) {{{ d[2] = 297 }}} km
{{{ d[1] + d[2] = 243 + 297 }}}
{{{ d[1] + d[2] = 540 }}} km
OK