Question 734904
This problem is dealing with factorials

for example 3! = 3 * 2 * 1

with this in mind the problem states

90!/(90-10)!*10!  so we have

90!/80!*10!

divide top and bottom of fraction by 80! and we get

90*89*88*87*86*85*84*83*82*81 / 10*9*8*7*6*5*4*3*2*1