Answer:
0.0158 = 1.58% probability that all of them are under 18.
Step-by-step explanation:
Probability of independent events:
If three events, A, B and C are independent, the probability of all happening is the multiplication of the probabilities of each happening, that is:

The percentage of people under the age of 18 was 23.5% in New York City, 25.8% in Chicago, and 26% in Los Angeles.
This means that 
If one person is selected from each city, what is the probability that all of them are under 18?
Since the three people are independent:

0.0158 = 1.58% probability that all of them are under 18.
Just pretend it’s a 3d right angle triangle and find the length of the hypotenuse.
d = sqrt(6^2 + 10^2 + 15^2) = 19
When you square a negative number, the result is positive.
(-4)^2 = (-4)ª(-4) = 16
When you cube a negative number, the result is negative.
(-4)^3 = (-4)•(-4)•(-4) = -64
Negatives pair up and cancel out, so odd exponents always have one negative unpaired, making the result negative.