Answer:
7 girls can go in the first place, 6 in the second, etc.
7! ways is the number of ways to arrange the girls.
likewise the boys can be arranged in 7! ways
The total number of ways becomes 7! * 7!
7! * 7! = 25,401 600 ways
To solve for this, set up a proportion.
21/40 = x/100.
Cross multiply the fraction's numerators with the denominators;
21 x 100, 40 and x.
2100/40x.
Divide both numbers by 40 to get x.
2100/40 = 52.5
21 is 52.5% of 40.
I hope this helps!
The given MGF is that for a random variable following a Poisson distribution with parameter

.
This means

, and

has PMF

So, the desired probability is

This is equivalent to
I=PRT, P=$1600 R=3% T=1yr
=1600x(3/100)x1
= $48.00