Question 1015062
Let {{{ d }}} = distance of the one-way trip in km
Let {{{ s }}} = the speed of the boat in still water in km/hr
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Equation for traveling with the current:
(1) {{{ d = ( s + 4 )*2 }}}
Equation for traveling against the current:
(2) {{{ d = ( s - 4 )*3 }}}
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(1) {{{ d = 2s + 8 }}}
(1) {{{ d - 2s = 8 }}}
and
(2) {{{ d = 3s - 12 }}}
(2) {{{ -d + 3s = 12 }}}
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Add (1) and (2)
(1) {{{ d - 2s = 8 }}}
(2) {{{ -d + 3s = 12 }}}
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{{{ s = 20 }}}
and
(1) {{{ d - 2s = 8 }}}
(1) {{{ d - 2*20 = 8 }}}
(1) {{{ d = 48 }}}
The speed of the boat in still water is 20 km/hr
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check:
(1) {{{ d = ( s + 4 )*2 }}}
(1) {{{ 48 = (20 + 4 )*2 }}}
(1) {{{ 48 = 24*2 }}}
(1) {{{ 48 = 48 }}}
OK
(2) {{{ d = ( s - 4 )*3 }}}
(2) {{{ 48 = ( 20 - 4 )*3 }}}
(2) {{{ 48 = 16*3 }}}
(2) {{{ 48 = 48 }}}
OK