Question 919369
Let {{{ a }}} = number of brown bears
Let {{{ b }}} = number of black bears
Let {{{ c }}} = number of white bears
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(1) {{{ a = 2b }}}
(2) {{{ c = (1/2)*b }}}
(3) {{{ a + b + c = 1288 }}}
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Substitute (1) and (2) into (3) 
(3) {{{ 2b + b + (1/2)*b = 1288 }}}
(3) {{{ ( 6/2 )*b + (1/2 )*b = 1288 }}}
(3) {{{ ( 7/2 )*b = 1288 }}}
(3) {{{ 7b = 2576 }}}
(3) {{{ b = 368 }}}
and
(1) {{{ a = 2b }}}
(1) {{{ a = 2*368 }}}
(1) {{{ a = 736 }}}
and
(2) {{{ c = (1/2)*b }}}
(2) {{{ c = ( 1/2 )*368 }}}
(2) {{{ c =184 }}}
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736 = number of brown bears
368 = number of black bears
184 = number of white bears
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check:
(3) {{{ a + b + c = 1288 }}}
(3) {{{ 736 + 368 + 184 = 1288 }}}
(3) {{{ 1288 = 1288 }}}
OK