Question 979632
Let {{{ s }}} = the number of sister's carl has
Let {{{ b }}} = the number of brother's Carl has
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His younger sister has {{{ b + 1 }}} brothers
( Carl has to be included )
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His younger sister has {{{ s - 1 }}} sisters
( she doesn't include herself )
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Equation for Carl's younger sister:
(1) {{{ b + 1 = 2*( s - 1 ) }}}
Equation for Carl:
(2) {{{ s = 2b }}}
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(1) {{{ b + 1 = 2s - 2 }}}
Substitute (2) into (1)
(1) {{{ b + 1 = 2*2b - 2 }}}
(1) {{{ b + 1 = 4b - 2 }}}
(1) {{{ 3b = 3 }}}
(1) {{{ b = 1 }}}
and
(2) {{{ s = 2b }}}
(2) {{{ s = 2*1 }}}
(2) {{{ s = 2 }}}
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The total number of children is:
{{{ b + 1 + s = 1 + 1 + 2 }}}
{{{ 1 + 1 + 2 = 4 }}}
4 children
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check:
(1) {{{ b + 1 = 2*( s - 1 ) }}}
(1) {{{ 1 + 1 = 2*( 2 - 1 ) }}}
(1) {{{ 2 = 2 }}}
OK