Ten per cent of bulbs produced by a factory are defective. A sample of 400 bulbs is taken.
The mean number of defective bulbs is:
(A) 0.4
(B) 10.0
(C) 40.0
(D) 360.0

The variance for the distribution of defective bulbs is:
(A) 36.0
(B) 20.0
(C) 6.0
(D) 3.6