Question 1029441
Let {{{ d }}} = Dorothy's age
Let {{{ w }}} = William's age
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(1) {{{ d = w + 9 }}}
(2) {{{ d*w = 360 }}}
Substitute (1) into (2)
(2) {{{ ( w+9 )*w = 360 }}}
(2) {{{ w^2 + 9w - 360 = 0 }}}
(2) {{{ ( w - 15 )*( w + 24 ) = 0 }}} ( by looking at it )
(2) {{{ w = 15 }}} ( can't use the negative root )
and
(1) {{{ d = w + 9 }}}
(1) {{{ d = 15 + 9 }}}
(1) {{{ d = 24 }}}
Dorothy is 24
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check:
(2) {{{ d*w = 360 }}}
(2) {{{ 24*15 = 360 }}}
(2) {{{ 360 = 360 }}}
OK