Question 677539
You need 2 equations- one for Norma
and one for Marietta
Let {{{ t }}} = time for both
Let {{{ s }}} = the speed of Norma's boat
{{{ s + 15 }}} = speed of Marietta's boat
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Norma's equation:
(1) {{{ 12 = s*t }}}
Marietta's equation:
(2) {{{ 36 = ( s + 15 )*t }}}
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(2) {{{ 36 = s*t + 15t }}}
Substitute (1) into (2)
(2) {{{ 36 = 12 + 15t }}}
(2) {{{ 15t = 24 }}}
(2) {{{ t = 1.6 }}}
and, since
(1) {{{ 12 = s*t }}}
(1) {{{ 12 = s*1.6 }}}
(1) {{{ s = 7.5 }}}
Norma is rowing at 7.5 mi/hr
check:
(2) {{{ 36 = ( s + 15 )*t }}}
(2) {{{ 36 = ( 7.5 + 15 )*t }}}
(2) {{{ 36 = 22.5*t }}}
(2) {{{ t = 36/22.5 }}}
(2) {{{ t = 1.6 }}}
OK