what is true for poisson distribution?
a.
mean and variance are always equal
b.
mean always greater than variance
c.
mean always smaller than variance
d.
none of the above

Option 'a' is correct.

Step-by-step explanation:

Poisson distribution is used when the number of successes are independent and success that occur in interval must be same in all intervals and of equal size.

In poisson distribution,

Mean  is always equal to variance.

Mathematically it is expressed as

E[x]=V[x].

So, Option 'a' is correct.