Formula for combinations:
C(n,r)=frac{n!}{r!(n-r)!}C(n,r)=n!r!(n−r)!
Let n=10n=10, and let r=6r=6
C(10,6)=frac{10!}{6!(10-6)!}C(10,6)=10!6!(10−6)!
=frac{10!}{6!*4!}=10!6!⋅4!
=frac{10*9*8*7*6*5*4*3*2*1}{6*5*4*3*2*1*4*3*2*1}=10⋅9⋅8⋅7⋅6⋅5⋅4⋅3⋅2⋅16⋅5⋅4⋅3⋅2⋅1⋅4⋅3⋅2⋅1
=frac{10*color(blue)(9)*color(green)(8)*7*cancel(6*5)*cancel(4*3*2*1)}{cancel(6*5)*color(green)(4)*color(blue)(3)*color(green)(2)*1*cancel(4*3*2*1)}
=frac{10*3*7}{1}
=210