Question 1121729
use formula:


{{{C}}}({{{n}}},{{{r}}})={{{n!/(r!(n-r)!)}}}


in your case {{{n=8}}} or {{{7}}} and {{{r=n}}}


so you have:


{{{8!/(n!(8-n)!)=4*(7!/(n!(7-n)!))}}}


{{{8!/7!=4*((n!(8-n)!)/(n!(7-n)!))}}}


{{{8=4*((8-n)!)/(7-n)!)}}}


{{{2=((8-n)!)/(7-n)!)}}}


{{{2=8 - n}}}


{{{n=8-2}}}


{{{n=6}}}


check: {{{8!/(6!(8-6)!)=4*(7!/(6!(7-6)!))}}} is true