Question 637048
Let {{{ w }}} = the speed of the wind in mi/hr
Let {{{ p }}} = the speed of the plane in still air
{{{ p + w }}} = the plane's speed going with the wind
{{{ p - w }}} = the plane's speed going against the wind
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Equation going with the wind:
(1) {{{ 1386 = ( p + w )*9 }}}
Equation going against the wind:
(2) {{{ 1386 = ( p - w )*11 }}}
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(1) {{{ 154 = p + w }}}
(1) {{{ p = 154 - w }}}
Substitute this result into (2)
(2) {{{ 126 = p - w }}}
(2) {{{ 126 = 154 - w - w }}}
(2) {{{ 126 - 154 = -2w }}}
(2) {{{ -28 = -2w }}}
(2) {{{ w = 14 }}}
Substitute this result into (1) or (2)
(2) {{{ 126 = p - 14 }}}
(2) {{{ p = 126 + 14 }}}
(2) {{{ p = 140 }}}
The plane's speed in still air is 140 mi/hr
The speed of the wind is 14 mi/hr
check:
(1) {{{ 1386 = ( 140 + 14 )*9 }}}
(1) {{{ 1386 = 154*9 }}}
(1) {{{ 1386 = 1386 }}}
OK