Calculate the duration between the following pairs of times: 1) 2:15 p.m. to 2:50 p.m., 2) 1:20 p.m. to 2:30 p.m., 3) 2:25 p.m. to 3:10 p.m.

$$2 \text{ hours } 50 \text{ minutes} - 2 \text{ hours } 15 \text{ minutes}$$ $$= (2-2) \text{ hours } (50-15) \text{ minutes}$$ $$= 0 \text{ hours } 35 \text{ minutes}$$

The duration is $\boxed{\text{35 minutes}}$.

2. Duration from 1:20 p.m. to 2:30 p.m.

to 2:00 p.m.

$$2 \text{ hours } 00 \text{ minutes} - 1 \text{ hour } 20 \text{ minutes}$$ $$= (1 \text{ hour } 60 \text{ minutes}) - (1 \text{ hour } 20 \text{ minutes})$$ $$= 40 \text{ minutes}$$

to 2:30 p.m.

$$40 \text{ minutes} + 30 \text{ minutes} = 70 \text{ minutes}$$

Alternatively, this is 1 hour and 10 minutes.
The duration is $\boxed{\text{1 hour 10 minutes}}$.

3. Duration from 2:25 p.m. to 3:10 p.m.

to 3:00 p.m.

$$3 \text{ hours } 00 \text{ minutes} - 2 \text{ hours } 25 \text{ minutes}$$ $$= (2 \text{ hours } 60 \text{ minutes}) - (2 \text{ hours } 25 \text{ minutes})$$ $$= 35 \text{ minutes}$$

to 3:10 p.m.

$$35 \text{ minutes} + 10 \text{ minutes} = 45 \text{ minutes}$$

The duration is $\boxed{\text{45 minutes}}$.