Question

2
In a class of
25
25 students,
3
5
5
3
​
of the class are boys,
2
5
5
2
​
of the class have ​blonde hair, and
1
5
5
1
​
of the class are boys with blonde hair.

​

​If one student is ​to be chosen at random from the class, what is the probability that the ​student is a boy or has blonde hair?

​Show your work on the scratchpad.

​

​P (boy or blonde hair) =

Answer 1

Total students = 25.
Boys = (3/5)·25 = 15.
Blonde = (2/5)·25 = 10.
Both (boys with blonde hair) = (1/5)·25 = 5.

Use inclusion–exclusion:
Number with (boy or blonde) = boys + blonde − both
= 15 + 10 − 5 = 20.

Probability = 20/25 = 4/5 = 0.8 = 80%.

So P(boy or blonde hair) = 4/5.