Question 268892
10/34 * 17/19 * 19/20 = 
= (10*17*19)/(34*19*20)
Cancel the 19s
= (10*17)/(34*20)
The 10s are obvious, cancel the 10 and 20 = 2*10
= 17/(34*2)
Cancel the 17s
= 1/4
Now don't you feel silly, talking about "large" numbers?