Question 857337
Let {{{ s }}} = the bus's speed on the winding road
{{{ s + 20 }}} = the bus's speed on the level road
Let {{{ d }}} = distance traveled on the winding road
{{{ 452 - d }}} = distance traveled on the level road
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Equation for level road:
(1) {{{ 452 - d = ( s + 20 )*5 }}}
Equation for winding road:
(2) {{{ d = s*3 }}}
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Substitute (2) into (1)
(1) {{{ 452 - 3s = ( s + 20 )*5 }}}
(1) {{{ 452 - 3s = 5s + 100 }}}
(1) {{{ 8s = 352 }}}
(1) {{{ s = 44 }}}
and
(2) {{{ d = s*3 }}}
(2) {{{ d = 44*3 }}}
(2) {{{ d = 132 }}}
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(1) {{{ 452 - d = ( s + 20 )*5 }}}
The average speed for the level road is:
{{{ s + 20 = 44 + 20 }}}
{{{ s + 20 = 64 }}} mi/hr
check:
(1) {{{ 452 - d = ( s + 20 )*5 }}}
(1) {{{ 452 - 132 = ( 44 + 20 )*5 }}}
(1) {{{ 320 = 64*5 }}}
(1) {{{ 320 = 320 }}}
and
(2) {{{ d = s*3 }}}
(2) {{{ 132 = 44*3 }}}
(2) {{{ 132 = 132 }}}
OK