Question 1047076
Let {{{ a }}} = ml of 5% NaCl solution
Let {{{ b }}} = ml of 15% NaCl solution
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(1) {{{ a + b = 200 }}}
(2) {{{ ( .05a + .15b ) / 200 = .12 }}}
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(2) {{{ .05a + .15b = 24 }}}
(2) {{{ 5a + 15b = 2400 }}}
(2) {{{ a + 3b = 480 }}}
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Subtract (1) from (2)
(2) {{{ a + 3b = 480 }}}
(1) {{{ -a - b = -200 }}}
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{{{ 2b = 280 }}}
{{{ b = 140 }}}
and
(1) {{{ a + b = 200 }}}
(1) {{{ a + 140 = 200 }}}
(1) {{{ a = 60 }}}
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60 ml of 5% NaCl solution is needed
140 ml of 15% NaCl solution is needed
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check:
(2) {{{ ( .05a + .15b ) / 200 = .12 }}}
(2) {{{ ( .05*60 + .15*140 ) / 200 = .12 }}}
(2) {{{ ( 3 + 21 ) / 200 = .12 }}}
(2) {{{ 24 = .12*200 }}}
(2) {{{ 24 = 24 }}}
OK