Exercise 3.29. In a school there are four kindergarten classes, with 21, 24, 17 and 28 students. We choose one of the 90 kindergarten students randomly, and denote the number of students in her class by X. Find the expectation and variance of X.

Expected mean = 23.2159

Variance = 15.89

Step-by-step explanation:

Given that :

Number of kindergarten students (X) :

21 + 24 + 17 + 28 = 90

P(X):

21/ 90 = 0.233

24/90 = 0.2667

17/90 = 0.1889

28/90 = 0.3111

X : 21 24 17 28

P(x) : _ 0.233 _ 0.2667 __ 0.1889 __ 0.3111

E(X) = Σ[(p)*p(x)]

(21 * 0.233) + (24 * 0.2667) + (17 * 0.1889) + (28 * 0.3111) = 23.2159

Var(X) : Σ(x²*p(x)) - E(x)²

x² * p(x) = (21^2 * 0.233) + (24^2 * 0.2667) + (17^2 * 0.1889) + (28^2 * 0.3111) - 23.2159^2

554.8667 - 538.97801281

= 15.88868719

= 15.89

my acc plz

step-by-step explanation:

if gloria has "carry over" minutes, (that is, any minutes paid for but not used in a month can be applied to her payment for minutes in the next month,) her total usage for the three months is: total minutes = 320 + 243 + 489 = 1052 minutes number of 200 minute blocks = 1052/200 = 5 r52 (that is 5 with a remainder of 52) rounding up the number of 200 minute blocks gives her usage for the three months as 6 blocks. the cost for six blocks is 6 x $25 = $150 she also has 200 - 52 or 148 carry over minutes if gloria pays each month and unused minutes are lost, applying the rounding up procedure to each month gives: first month usage of 320 minutes rounds up to 2 blocks of 200 minutes for a payment of 2 x $25 = $50 second month usage of 243 minutes rounds up to 2 blocks of 200 minutes for a payment of 2 x $25 = $50 third month usage of 489 minutes rounds up to 3 blocks of 200 minutes for a payment of 3 x $25 = $75 total payments for the three months are $50 + $50 + $75 = $175 get the plan with carry over minutes!