# Statistics (random variable)

posted by
**pallavi**
.

A contractor is interested in the total cost of a project on which he intends to bid. He estimates that materials will cost rs 25,000 and that his labour will be rs900 per day. If he the project takes X days to complete,the total cost of the project (in rupees) will be given as:

c=25,000+900x

there is a table which gives the completion time, in days, for theproject.

Completion time X (days) : Probability

10 : 0.1

11 : 0.3

12 : 0.3

13 : 0.2

14 : 0.1

Find the mean and variance for completion time X.

For mean which is E(x) : i got 11.9

Variance V(x): i got 176.7

standard deviation (x), i got 5.92

Now find the mean and variance for total cost C.

C=25,000+900x

Mean= c=25000 +900x

E(c)=E(25000+900)

=(25000+ 900 v(x)

25000 + 900x

E(x) =11.9

=25000+900 x 11.9

=357,10

but am having problem to find the variance??

help pls!