Question 1097767
Let {{{d}}} = the distance from A to B
{{{ d - 30 }}} = the distance in km the truck travels 
until it meets the car
{{{ d + 30 }}} = the distance in km the car travels
until it meets the truck
Let {{{ t }}} = time in hrs until they meet
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The truck's equation:
(1) {{{ d - 30 = 40t }}}
The car's equation:
(2) {{{ d + 30 = 50t }}}
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subtract (1) from (2)
(2) {{{ d + 30 = 50t }}}
(1) {{{ -d + 30 = -40t }}}
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{{{ 60 = 10t }}}
{{{ t = 6 }}} hrs
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Plug this result back into either equation
(1) {{{ d - 30 = 40*6 }}}
(1) {{{ d = 240 + 30 }}}
(1) {{{ d = 270 }}}
The distance between the towns is 270 km
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check:
(2) {{{ d + 30 = 50t }}}
(2) {{{ 270 + 30 = 50*6 }}}
(2) {{{ 300 = 300 }}}
OK