Question 1081850
nCr = n!/((n-r)!*r!)    ("Combinations" or ways to arrange objects when order doesn't matter)
where:  
            n! = n*(n-1)*(n-2)*…*3*2*1    (I leave off the *1 when solving problems, it doesn't change anything)

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Expression 1:
{{{ 9C2 = 9!/((9-2)!*(2!)) =  (9*8*7*6*5*4*3*2)/((7*6*5*4*3*2)*2) = (9*8)/2 = 36 }}}

Because I've seen these before, if I were writing it out, I'd say to myself 9*8 (because 7, 6, …, 2 will cancel from the (9-2)! = 7! part),  divided by 2!=2:
{{{ 9C2 = 9*8/2! = 36 }}}
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For expression 2, using the shortcut,  {{{ 70C3 = 70!/((67!)*(3!)) = (70*69*68)/(3*2) = 54740 }}}