Question 421537
Let {{{s}}} = it's usual speed in mi/hr
Let {{{t}}} = it's usual time in hrs
given:
(1) {{{ 4000 = s*t }}}
(2) {{{ 4000 = (s - .15s)*(t + .5) }}}
--------------------
(2) {{{ 4000 = .85s*(t + .5) }}}
(2) {{{ 4000 = .85s*t + .425s }}}
By substitution:
(2) {{{ 4000 = .85*4000 + .425s }}}
(2) {{{.425s = 4000 - .85*4000 }}}
(2) {{{.425s = .15*4000 }}}
(2) {{{.425s = 600 }}}
(2) {{{ s = 1411.765 }}} mi/hr
check answer:
(1) {{{ 4000 = s*t }}}
(1) {{{ t = 4000/1411.765 }}}
(1) {{{ t = 2.833 }}} hrs
and
(2) {{{ 4000 = .85s*(t + .5) }}}
(2) {{{ 4000 = .85*1411.765*(2.833 + .5) }}}
(2) {{{ 4000 = 1200.00025*3.333 }}}
(2) {{{ 4000 = 3999.6 }}}
close enough