<PRE><B>Question 1140432</B>
Let {{{ a }}} = number of 20 cent coins
Let {{{ b }}} = number of 50 cent coins
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(1) {{{ a + b = 11 }}}
(2) {{{ 20a + 50b = 310 }}} ( in cents )
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(2) {{{ 2a + 5b = 31 }}}
Multiply both sides of (2) by {{{ 2 }}}
and subtract (1) from (2)
(2) {{{ 2a + 5b = 31 }}}
(1) {{{ -2a - 2b = -22 }}}
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{{{ 3b = 9 }}}
{{{ b = 3 }}}
and
(1) {{{ a + 3 = 11 }}}
(1) {{{ a = 8 }}}
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She has 8 of the 20 cent coins and
3 of the 50 cent coins
check:
(2) {{{ 2*8 + 5*3 = 31 }}}
(2) {{{ 16 + 15 = 31 }}}
(2) {{{ 31 = 31 }}}
OK</PRE>