Question 275485
nCr=combination: n things taken r at a time=n!/((n-r)!r!)
.
a)
5C2/20C2
=10/190
=1/19  probability both are blue.
.
b)
15C2/20C2 probability none are blue
=105/190
=21/38
1- 21/38 = 17/38  probability at least 1 is blue.
.
Ed