Probability of meeting ( II )

[Guest]

A boy will arrive at a coffee shop randomly from 1 pm to 1.40 pm . He will stay for 20 mins and then leave .
A girl will arrive at the coffee shop randomly from 1 pm to 1.50 pm . She will stay for 10 mins and then leave .
A teacher will pass through the coffee shop randomly from 1 pm to
1.30 pm . Find
(1) The probability that the teacher will meet the boy .
(2) The probability that the teacher will meet the girl .
(3) The probability that all the 3 people will meet .

[Guest]

The answer for (1) is 1/2 .
The answer for (2) is 1/5 .
The 3rd one is still under consideration .