Question 598753
{{{ s }}} = number of Sons
Stephen is 1 of the Sons, so he has {{{ s - 1 }}} brothers
{{{ d }}} = number of daughters, which is number of sisters he has
given:
(1) {{{ d = 2*( s - 1 ) }}}
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Sarah is one of the daughters, so she has
{{{ d - 1 }}} sisters
The number of her brothers is the number of Sons
given:
(2) {{{ s = d - 1 }}}
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From (2),
(2) {{{ d = s + 1 }}}
Substitute (2) into (1)
(1) {{{ s + 1 = 2s - 2 }}}
(1) {{{ s = 3 }}} 
and
(2) {{{ d = s + 1 }}}
(2) {{{ d = 4 }}}
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(B)
Stephen has {{{ d = 4 }}} sisters
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(C)
Sarah has {{{ d - 1 = 3 }}} sisters
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(D)
Stephen has {{{ s - 1 = 2 }}} brothers
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(E)
Sarah has {{{ s = 3 }}} brothers