Question

Nina goes to the supermarket 0, 1, or 2 times in a week. The probability that she goes 0 days is 0.2, the probability that she goes 1 day is 0.50, and the probability that she goes 2 days is 0.30. What is the expected value of the number of days per week on which Nina goes to the supermarket? 0.8

Answer 1

The probability that Nins goes 0 days is 0.2, the probability that she goes 1 day is 0.50, and the probability that she goes 2 days is 0.30. You can write these data as a table:

$\begin{array}{cccc} x_i & 0 & 1 & 2 \\ p_i & 0.2 & 0.5 & 0.3 \end{array}$

where $x_i$ are numbers of days and $p_i$ are probabilities.

The expected value of the number of days per week on which Nina goes to the supermarket is

$E(X)=\sum\limits_{i=1}^3x_ip_i=0\cdot 0.2+1\cdot 0.5+2\cdot 0.3=0.5+0.6=1.1$.

Answer: the expected value of the number of days per week on which Nina goes to the supermarket is 1.1.