More on Time & Speed

Time in Minutes

To convert hours and minutes to minutes, the hours are multiplied by 60 and the minutes added.

Example: 6 h 52 m

(6 x 60) + 52 = 360 + 52 = 412 m or min

To change minutes to hours and minutes divide by 60 and note the number left over as minutes.

Example: 132 m = (132/60) = 2 h and 12 (left over). Proper notation would be 2 h 12 m.

Or,

If the answer is taken to one or more decimal places, the tenths can be multiplied by 60 and rounded, if necessary : for example, 132/60 = 2.2 hours or 2 h + (0.2 x 60) = 2h + 12 m
or 2 h 12 m

Example: Convert 752 m to hours and minutes:

752 m ÷ 60 = 12.53 h

since 12h x 60 = 720 m

then 752 m- 720 m = 32m

12 h 32 m

 OR

Another method:

752 m ÷ 60 = 12.53 h

0.53 x 60 = 31.8 m which rounds to

32 m

then 12 h + 32m = 12h 32m.

Adding and Subtracting Time

To work with time, calculate hours and minutes separately. Divide hours by 60 to get minutes, either as minutes left over the whole number, or as fractions of an hour.

Example: Calculate hours and minutes of: 424 m plus 3 h 45 m:

First: 424 m / 60 = 7 h 4 m
Then, add this to....3 h 45 m

The answer is: 10 h 49 m

Example: What time is it 2 h 55 m earlier than 0820?

Calculate hours: 8 h - 2 h = 6 h or 0600

Calculate minutes : 20 m - 55 m= -35 m Subtract the "minus 35" from 0600:

0600 - 0035 m = 0525

Working with Speed

To calculate average speed in one hour of motoring or sailing:

Multiply speed by the duration and repeat for the other periods, add their products together, and divide the total by 60. A formula for this is:

Avg. Speed = [(S1 x min) + (S2 x min) + ...+] ÷ 60, where S1 is the speed in the first period, S2 the speed in the second period and min is the duration at that speed.

For example, consider speeds and duration of:

5 knots for 20 minutes , 3 knots for 10 minutes, 6 knots for 30 minutes =

[(5 x 20) + (3 x 10) + (6 x 30)] ÷ 60 = [100 + 30 + 180] ÷ 60

310 ÷ 60 = 5.16, rounded to 5.2 knots

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