Question 1127974
Let {{{ a }}} = the number of girls
Let {{{ b }}} = the number of boys
--------------------------------------
(1) {{{ a - 1 = b }}}
(2) {{{ 2*( b - 1 ) = a }}}
---------------------------
Note that when I am counting a girls sisters,
I count them as {{{ a - 1 }}}
When counting a boys brother's, I count them as
{{{ b - 1 }}}
---------------------------
Plug (1) into (2)
(2) {{{ 2*( a - 1 - 1 ) = a }}}
(2) {{{ 2a - 4 = a }}}
(2) {{{ a = 4 }}}
and
(1) {{{ a - 1 = b }}}
(1) {{{ 4 - 1 = b }}}
(1) {{{ b = 3 }}}
---------------------
There are 4 girls and 3 boys
--------------------------------
check:
Each girl has as many sisters as brothers TRUE
Each boy has twice as many sisters as brothers TRUE