Let X be the random variablevalue of chosen coinand let M be the random variablemoney child gets. Let A be the age of the child.

Then and so .

Assuming replacement of coin, Pr(X = 10 pence) = 7/10 and Pr(X = 20 pence) = 3/10.

Calculate E(X).

Substitute child's age and value of E(X) into E(M).