Question 885920
Let {{{ d }}} = the one-way distance traveled
Let {{{ t[1] }}} = time in hrs to travel downstream
Let {{{ t[2] }}} = time in hrs to travel upstream
Going downstream, Len can travel at a rate of: 
{{{ 3 + 2 = 5 }}} mi/hr
Going upstream, Len can travel at a rate of: 
{{{ 3 - 2 = 1 }}} mi/hr
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Going downstream:
(1) {{{ d = 5t[1] }}}
Going upstream:
(2) {{{ d = 1*t[2] }}}
Also given:
(3) {{{ t[1] + t[2] = 3 }}}
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From (1) and (2):
(2) {{{ t[2] = 5t[1] }}}
and
(3) {{{ t[1] + 5t{1] = 3 }}}
(3) {{{  6t[1] = 3 }}}
(3) {{{ t[1] = .5 }}} hr
and
(3) {{{ 1/2 + t[2] = 3 }}}
(3) {{{ t[2] = 2.5 }}} hrs
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He can spend 1/2 hr going downstream
and
(1) {{{ d = 5t[1] }}}
(1) {{{ d = 5*(1/2) }}}
(1) {{{ d = 2.5 }}} mi
He can travel 2.5 mi downstream
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check:
(2) {{{ d = 1*t[2] }}}
(2) {{{ d = 1*2.5 }}}
(2) {{{ d = 2.5 }}} mi
OK