20 chips numbered 1 through 20 are placed into an urn The ch

20 chips numbered 1 through 20 are placed into an urn. The chips are then selected one by one, without replacement, until all 20 have been selected. What is the probability that the numerical values of the 3rd, 15th, and 19th chips are increasing?

Solution

Odd numbers in 1 to 20 is 10. Exhaustive no: of cases = 20c3=1140 and favourable no: of cases without replacement is 10c1*9c1*8c1=(10*9*8)=720. Then probability that the numerical values of the 3rd, 15th, and 19th chips are increasing = 720/1140=.6316.