Telling Time Worksheet-19: Solve time-related word problems.

Let’s solve each problem one by one.

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Problem (1):
The runner finished at 10:40 p.m. It took 21 hours. When did he start?

We need to go *back* 21 hours from 10:40 p.m.

First, let’s break 21 hours into parts:
- 21 hours = 24 hours – 3 hours → so going back 21 hours is like going back almost a full day, but not quite.
- Alternatively, we can subtract 21 hours directly.

Start from 10:40 p.m. and go back 21 hours:

Go back 10 hours → 12:40 p.m. (same day)
Go back another 11 hours → that’s 1:40 a.m. (previous day)

Wait — let’s do it more carefully:

From 10:40 p.m., subtract 21 hours:

Step 1: Subtract 10 hours → 12:40 p.m. (still same day)
Step 2: Subtract 11 more hours → 1:40 a.m. (the day before)

But wait — 10 + 11 = 21, yes.

So 10:40 p.m. minus 21 hours = 1:40 a.m. the previous day.

But let’s verify with a different method:

Add 3 hours to 10:40 p.m. → that’s 1:40 a.m. next day.
Since 21 hours before is the same as 3 hours after in the past (because 24 - 21 = 3), then 21 hours before 10:40 p.m. is 3 hours before 10:40 p.m. on the *previous* day? No — better to think:

If you go back 21 hours from 10:40 p.m., you land at:

10:40 p.m. minus 21 hours = 1:40 a.m. (same calendar day? No — because 21 hours is more than half a day).

Actually:

10:40 p.m. is 22:40 in 24-hour time.

22:40 minus 21 hours = 1:40 → which is 1:40 a.m. on the same day? Wait — no:

22:40 minus 21 = 1:40 → that’s 1:40 a.m. on the *same* day? That doesn’t make sense because 22:40 is late evening.

Wait — if today is Day X, and it’s 10:40 p.m. on Day X, then 21 hours earlier would be on Day X-1.

Let’s calculate:

From 10:40 p.m. Day X, go back 21 hours:

- Back 10 hours → 12:40 p.m. Day X
- Back 11 more hours → 1:40 a.m. Day X-1

Yes! So the start time was 1:40 a.m. the day before the finish.

But the question doesn’t specify date, just “when” — so we can say 1:40 a.m. (assuming same cycle, but actually it’s the prior day).

In time problems like this, we usually just give the time, not the date, unless specified.

So answer: 1:40 a.m.

Wait — let me double-check:

If he started at 1:40 a.m., and ran 21 hours:

1:40 a.m. + 21 hours = 1:40 a.m. + 21 = 22:40 → which is 10:40 p.m. Yes! Perfect.

So correct answer for (1): 1:40 a.m.

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Problem (2):
Your watch stopped 4 hours ago. The correct time now is 12:00 p.m. What time did your watch stop?

“Stopped 4 hours ago” means the watch shows the time it was 4 hours ago.

Current time: 12:00 p.m.

Subtract 4 hours: 12:00 p.m. – 4 hours = 8:00 a.m.

So the watch stopped at 8:00 a.m.

Check: If it stopped at 8:00 a.m., and now it’s 12:00 p.m., that’s 4 hours later — correct.

Answer: 8:00 a.m.

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Problem (3):
Birthday party is at 1:14 a.m. You need 7 hours to make the cake. When should you start?

You need to finish by 1:14 a.m., and it takes 7 hours to make the cake.

So start time = 1:14 a.m. minus 7 hours.

1:14 a.m. minus 7 hours:

Go back 1 hour → 12:14 a.m.
Go back 6 more hours → 6:14 p.m. (previous day)

Or: 1:14 a.m. is 01:14 in 24-hour time.

01:14 – 7 = negative? So borrow 24 hours:

01:14 + 24:00 = 25:14
25:14 – 7:00 = 18:14 → which is 6:14 p.m.

Yes.

Check: Start at 6:14 p.m., add 7 hours → 6:14 + 7 = 13:14 → 1:14 a.m. next day. Correct.

Answer: 6:14 p.m.

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Problem (4):
If it will be 6:51 a.m. in 11 hours, what time is it now?

“Will be 6:51 a.m. in 11 hours” → so current time + 11 hours = 6:51 a.m.

So current time = 6:51 a.m. minus 11 hours.

6:51 a.m. is 06:51.

06:51 – 11 = negative → so add 24 hours:

06:51 + 24:00 = 30:51
30:51 – 11:00 = 19:51 → which is 7:51 p.m.

Check: 7:51 p.m. + 11 hours = 7:51 + 11 = 18:51? Wait no:

7:51 p.m. is 19:51.

19:51 + 11 = 30:51 → 30:51 - 24 = 6:51 a.m. next day. Correct.

Answer: 7:51 p.m.

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Final Answers:

(1) 1:40 a.m.
(2) 8:00 a.m.
(3) 6:14 p.m.
(4) 7:51 p.m.

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Final Answer:
(1) 1:40 a.m.
(2) 8:00 a.m.
(3) 6:14 p.m.
(4) 7:51 p.m.