Question

In a shipment of 7 items there are three defective items .At random 4 items are selected what is the expected number of defective items?


give the cuurect ansser

Answer 1

Answer:

Here at least 2 items are defective out of 4. So the no. of defective items can be 2 or defective can be 3.

Total no. of defective ites =3

If 2 items are defective =3C2×7C2=63

If 3 items are defective =3C3×7C1=7

Probability that atleast 2 out of 4 items are defective =10C463+7=21070=31