Use the formula (nr)=n!r! (n−r)!\binom{n}{r} = \dfrac{n!}{r!\,(n-r)!}(rn)=r!(n−r)!n! to show that (104)=210\binom{10}{4} = 210(410)=210.
144 exam-style questions on AQA A Level Maths 1.7.1 Binomial expansion. Each one has a worked solution and a mark scheme showing where the marks go.