Question 508036
Let {{{ s }}} = her speed before lunch
{{{ s + 10 }}} = her speed after lunch
{{{ 8 - 5 = 3 }}} hrs driving time after lunch
Let {{{ d }}} = distance she drove before lunch
{{{ 430 - d }}} = distance she drove after lunch
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Before lunch:
(1) {{{ d = s*5 }}}
After lunch:
(2) {{{ 430 - d = ( s + 10 )*3 }}}
Substitute (1) into (2)
(2) {{{ 430 - 5s = 3s + 30 }}}
(2) {{{ 8s = 430 - 30 }}}
(2) {{{ 8s = 400 }}}
(2) {{{ s = 50 }}}
She drove 50 mi/hr in the morning
check:
{{{ s + 10 = 60 }}}
(1) {{{ d = 5*50 }}}
(1) {{{ d = 250 }}}
and
(2) {{{ 430 - 250 = 60*3 }}}
(2) {{{ 180 = 180 }}}
OK