Question 988491
Let {{{ w }}}  = windspeed in mi/hr
Let {{{ s }}} = the speed of the plane in still air
{{{ s + w }}} = plane's speed going with the wind
{{{ s - w }}} = plane's speed going against the wind
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(1) {{{ 630 = ( s + w )*3 }}}
(2) {{{ 630 = ( s - w )*3.5 }}}
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(1) {{{ s + w = 210 }}}
(2) {{{ s - w = 180 }}} ( now add equations )
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{{{ 2s = 390 }}}
{{{ s = 195 }}}
and
(1) {{{ s + w = 210 }}}
(1) {{{ 195 + w = 210 }}}
(1) {{{ w = 15 }}}
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The windspeed is 15 mi/hr
The speed of th plane in still air is 195 mi/hr
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check:
(1) {{{ 630 = ( s + w )*3 }}}
(1) {{{ 630 = ( 195 + 15 )*3 }}}
(1) {{{ 630 = 210*3 }}}
(1) {{{ 630 = 630 }}}
and
(2) {{{ 630 = ( s - w )*3.5 }}}
(2) {{{ 630 = ( 195 - 15 )*3.5 }}}
(2) {{{ 630 = 180*3.5 }}}
(2) {{{ 630 = 630 }}}
OK