Page 166 - ICSE Math 4

15 min 45 min

6:45 p.m. 7:00 p.m. 8:00 p.m. 8:45 p.m.
We can see that there are 45 minutes between the two mes.

Mark it on the number line.
Step 4: Now count the number of hours le between 7:00 p.m. and
8:00 p.m. and mark it on the number line.

15 min 1 h 45 min
6:45 p.m. 7:00 p.m. 8:00 p.m. 8:45 p.m.
We can see that there is one hour le between the two mes.
Step 5: Calculate the elapsed me by wri ng the hours and minutes together.

15 min + 1 h + 45 min = 15 min + 45 min + 1 h

= 60 min + 1 h
= 1 h + 1 h (since 60 min = 1 h)
= 2 h

So, Manan took 2 hours to fi nish his homework.

Example 11: Look at the given clocks to fi nd the dura on
of me passed between the fi rst clock and
the second clock.
Solu on: Time shown by the fi rst clock = 4:25

Time shown by the second clock = 5:15

35 min 15 min
4:25 5:00 5:15
Dura on of me passed = 35 min + 15 min = 50 min

So, dura on of me passed = 50 minutes.

By addi on or subtrac on
Look at the examples to learn how to calculate elapsed me by addi on and subtrac on.

Example 12: A class test starts at 9:15 a.m. It is of 45 minutes dura on. When will it fi nish?

Solu on: Star ng me = 9:15 a.m. = 9 h 15 min
Calcula on
Dura on = 45 min h min

Finishing me = 9 h 15 min + 45 min = 9 h + 15 min + 45 min 9 15

= 9 h + 60 min (we know that 60 min = 1 h) + 45
1
= 9 h + 1 h = 10 h 9 60

= 10:00 a.m. 10 00
So, the test will fi nish at 10:00 a.m.

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