if the US Senate, with 100 members, contains 20 more Democrat's than Republicans how many Democrat's does it contain?
100=d+(d-20)
First add 20 to both sides.
120=d+d
Now divide the sides by 2.
D=60
There are 60 democrats.
100=60+(60-20)
100=60+40
there are 60 democrats and 40 republicans