Subtracting Time
Time tells us about the duration of a task or an event.
We measure time in hours, minutes, and seconds. There are 60 minutes in an hour and 60 seconds in a minute.
Subtracting hours and minutes
Here are the steps to subtract time (4 hours 45 minutes  2 hours 20 minutes) given in hours and minutes.
Step I: Check if the minutes of the first time (4 hours 45 minutes) is less than the minutes of the second time (2hour 20 minutes). If that is the case then,
 Take one away from the hours of the first time.
 Add 60 to the minutes of the first time.
(Since 45 is not less than 20, we move on to the next step)
Step II: Subtract the minutes. (45 minutes  20 minutes = 25 minutes)
Step III: Subtract the hours. (4 hours  2 hours = 2 hours)
Hence, the resultant from Step II and Step III together is the answer (2hours 25minutes).
Example 1: Solve the following
 7 hours 45 minutes – 6 hours and 15 minutes.
 7 hours 15 minutes – 6 hours and 45 minutes
Solution:
A.
Step I: Since 45 is not less than 15, we move on to the next step
Step II: On taking away the minutes, we get,
Step III: On taking away the hours, we get,
Hence, the answer is 1 hour and 30 minutes.
B.
Step I: Since 15 is less than 45, we take one away from the hours of the first time and add 60 to the minutes of the first time.
 7 – 1 = 6 hour
 15 + 60 = 75minutes
Step II: On taking away the minutes, we get,
Step III: On taking away the hours, we get,
Hence, the answer is 0 hours 30 minutes or just 30 minutes.
Clock
A clock is a device we use to measure time. Time on a clock tells us when a certain event occurs or finishes.
For example, the clock shows a time of 7 a.m.
Given below is a clock, the bigger hand is the minute hand and the shorter hand is the hour hand. The redcolored hand is the second hand.
Subtracting Clock Time
Here are the steps to subtract two times of a clock (4:45 pm – 2:20 pm):
Case I: If both the times are either in am or in pm
Step I: Check if the minutes of the first time (2:45 pm) is less than the minutes of the second time (2:20 pm). If that is the case then
 Take one away from the hours of the first time.
 Add 60 to the minutes of the first time.
(Since 45 is not less than 20, we move on to the next step)
Step II: Subtract the minutes. (45  20 = 25 minutes)
Step III: Subtract the hours. (4  2 = 2 hours)
Hence, the resultant from Step II and Step III together is the answer (2 hours 25 minutes).
Example 2: Solve the following
A: 8:15 pm6:45pm
Solution:
A. 8:15 pm6:45pm
Step I: Since 15 is less than 45, we take one away from the hours of the first time and add 60 to the minutes of the first time.
8  1 = 7 hour
15 + 60 = 75 minutes
Step II: On taking away the minutes, we get,
Step III: On taking away the hours, we get,
Hence, the answer is 1 hour and 30 minutes.
Case II: If one of the times is in am and the other is in pm (8:30 am – 2:10 pm), we will follow the below steps:
Step I: Take away hours of the first time (8:30 am) from 11 (11 – 8 = 3 hours) and also take away minutes of the first time from 60 (60  30 = 30 minutes).
Step II: Add hours obtained from Step I (3 hours) and hours of the second time (2:10 pm).
(3+2 = 5 hours)
Step III: Add minutes obtained from Step I (30 minutes) and minutes of the second time (2:10 pm).
(30 + 10 = 40minutes)
The answer to Step II and III together is our final answer (5 hours 40 minutes).
Example 3: Solve 10: 45 am – 2: 15 pm.
Solution:
Since one of the time is in am and the other time is in pm, steps of case II will be used.
Step I: On taking away hour and minutes of 10:45 am from 11 and 60 respectively, we get,
11 – 10 = 1 hour
60 – 45 = 15 minutes
Step II: On adding hours of 2:15 pm and hours obtained from step I, we get
1 + 2 = 3 hours
Step III: On adding minutes of 2:15 pm and minutes obtained from step I, we get,
15 + 15 = 30 min
Hence, the answer is 3 hours and 30 minutes.
Fun Fact
