Page 512
512.1 altogether, all together
Altogether is an adverb meaning “completely.” All together is used to describe people or things that are gathered in one place at one time.
The snow finally stopped altogether.
Dad was happy to have his children all together for Friday night supper.
512.2 among, between
Among is used when speaking of more than two persons or things. Between is used when speaking of only two.
The three friends talked among themselves as they tried to pick a favorite between Marvel and DC.
512.3 amount, number
The noun number is used for persons or things you can actually count. The noun amount is used for things you cannot count but can measure according to their whole effect.