Answer:
a) E(X)=1
b) σ=1
c) P(X>1)=0.368
d) P(2<X<5)=0.128
Step-by-step explanation:
We have X: "the time between two successive arrivals at the drive-up window of a local bank", exponentially distributed with λ = 1.
a) We have to compute the expected time between two successive arrivals.
The expected value for X as it is exponentially distributed is:

b) We have to compute the standard deviation of X.
The standard deviation is calculated as:

c) The probability that X is larger than 1 (P(X>1))
We can express the probability as:

d) The probability that X is between 2 and 5 (P(2<X<5))

Prob of selected students times prob of selecting boys times prob of selecting 3 boys
total students = 15b + 30g = 45 students
1. 10s/45t = 0.22
2. 15b/45t = 0.33
3. 3b/15b = 0.2
0.22×0.33×0.2=0.0148
1.48%
I'm not sure 100%... double check answer please
Carl is 2 yrs older than bob. Because Alan+Carl is 2 more than Alan+bob
So bob=16 and Carl is 18
16+18=34
And Alan is 24
P = 4x + 2y
additional info.
<span>x+2y <u><</u> 10
y <u><</u> 2
x <u>></u> 0
y <u>></u> 0
y can only be 0, 1, and 2.
x + 2(0) <u><</u> 10 = x <u><</u> 10
x + 2(1) <u><</u> 10 = x + 3 <u><</u> 10 = x <u><</u> 10 - 3 = x <u><</u> 7
x + 2(2) <u><</u> 10 = x + 4 <u><</u> 10 = x < 10 - 4 = x <u><</u> 6
x = 10 ; y = 0 : P = 4(10) + 2(0) = 40 + 0 = 40
x = 7 ; y = 1 : P = 4(7) + 2(1) = 28 + 2 = 30
x = 6 ; y = 2 : P = 4(6) + 2(2) = 24 + 4 = 28
The maximum value of P is 40. Where x is 10 and y is 0.</span>
This is what WolframAlpha says. Look at the image below.