Time intervals (how long) worksheet

Part A: Working out and filling in

1. 1. 7 o'clock → 10 o'clock = 3 hours

   7 o'clock → 10 o'clock: the hour hand counts on from 7 to 10: 8, 9, 10, 3 numbers; or 10 − 7 = 3, so 3 hours

2. 2. 3 o'clock → 7 o'clock = 4 hours

   3 o'clock → 7 o'clock: the hour hand counts on from 3 to 7: 4, 5, 6, 7, 4 numbers; or 7 − 3 = 4, so 4 hours

3. 3. 5 o'clock → 6 o'clock = 1 hours

   5 o'clock → 6 o'clock: the hour hand counts on from 5 to 6: 6, 1 numbers; or 6 − 5 = 1, so 1 hours

4. 4. 3 o'clock → 6 o'clock = 3 hours

   3 o'clock → 6 o'clock: the hour hand counts on from 3 to 6: 4, 5, 6, 3 numbers; or 6 − 3 = 3, so 3 hours

5. 5. 4 o'clock → 9 o'clock = 5 hours

   4 o'clock → 9 o'clock: the hour hand counts on from 4 to 9: 5, 6, 7, 8, 9, 5 numbers; or 9 − 4 = 5, so 5 hours

6. 6. 9 o'clock → 10 o'clock = 1 hours

   9 o'clock → 10 o'clock: the hour hand counts on from 9 to 10: 10, 1 numbers; or 10 − 9 = 1, so 1 hours

7. 7. 2 o'clock → 5 o'clock = 3 hours

   2 o'clock → 5 o'clock: the hour hand counts on from 2 to 5: 3, 4, 5, 3 numbers; or 5 − 2 = 3, so 3 hours

8. 8. 8 o'clock → 12 o'clock = 4 hours

   8 o'clock → 12 o'clock: the hour hand counts on from 8 to 12: 9, 10, 11, 12, 4 numbers; or 12 − 8 = 4, so 4 hours

9. 9. 7 o'clock → 12 o'clock = 5 hours

   7 o'clock → 12 o'clock: the hour hand counts on from 7 to 12: 8, 9, 10, 11, 12, 5 numbers; or 12 − 7 = 5, so 5 hours

10. 10. 5 o'clock → 10 o'clock = 5 hours

    5 o'clock → 10 o'clock: the hour hand counts on from 5 to 10: 6, 7, 8, 9, 10, 5 numbers; or 10 − 5 = 5, so 5 hours

11. 11. 3 o'clock → 9 o'clock = 6 hours

    3 o'clock → 9 o'clock: the hour hand counts on from 3 to 9: 4, 5, 6, 7, 8, 9, 6 numbers; or 9 − 3 = 6, so 6 hours

12. 12. 9 o'clock → 11 o'clock = 2 hours

    9 o'clock → 11 o'clock: the hour hand counts on from 9 to 11: 10, 11, 2 numbers; or 11 − 9 = 2, so 2 hours

Part B: Word problems

Marking: 2 for the working, 1 for the answer, 1 for the sentence.

1. 13. The doctor tells Ming to take medicine every 2 hours. He takes the first dose at 6 o'clock in the morning. At what o'clock should he take the 4th dose? (Answer: 12 o'clock)

   From the first dose to the 4th, there are only 3 gaps of 2 hours, not 4; 6 + 3 × 2 = 12

2. 14. Tsz-hin starts building a model kit at 4 o'clock and expects it to take 4 hours. It is now 6 o'clock. How many more hours of building are left? (Answer: 2 hours)

   Expected to finish: 4 + 4 = 8 o'clock; 8 − 6 = 2

3. 15. Tsz-ching goes to bed at 8 o'clock at night and gets up at 6 o'clock the next morning. How many hours does she sleep? (Answer: 10 hours)

   8 at night to 12 midnight: 12 − 8 = 4 hours; 12 midnight to 6 in the morning: 6 hours; 4 + 6 = 10

4. 16. The doctor tells Tsz-hin to take medicine every 2 hours. He takes the first dose at 8 o'clock in the morning. At what o'clock should he take the 3rd dose? (Answer: 12 o'clock)

   From the first dose to the 3rd, there are only 2 gaps of 2 hours, not 3; 8 + 2 × 2 = 12

5. 17. A public pool is open from 10 o'clock to 12 noon, then closes for a break and opens again from 1 o'clock to 6 o'clock. How many hours is it open each day altogether? (Answer: 7 hours)

   Before the break: 12 − 10 = 2 hours; After the break: 6 − 1 = 5 hours (the break doesn't count); 2 + 5 = 7

6. 18. Tsz-hin leaves home at 7 o'clock, spends 2 hours in the car getting to Grandma's, and stays there 3 hours before leaving. At what o'clock does he leave Grandma's? (Answer: 12 o'clock)

   Reaches Grandma's: 7 + 2 = 9 o'clock; 9 + 3 = 12