Question 1121413
Prob >$20 is 0.3
E(X)=0.2*10+0.5*20+0.2*50+0.1*100=$32
The expected value may be considered to be a weighted average, how much will be withdrawn on average. In other words, the expected value*the number of people withdrawing will be about what the total amount of money needed is.
variance is $22^2*0.2+$12^2*0.5+$18^2*0.2+$88^2*0.1=$96.80+$72+$64.80+$774.40=$1008
sd is sqrt (V)=$31.75