Time Subtraction

1.     11 h 45 min  −  6 h 15 min = _____ h ____ min

Step 1: Subtract the minutes.
    45 min  −  15 min
=  30 min

Step 2: Subtract the hours.
    11 h  −  6 h
=  5 h

So,
    11 h 45 min  −  6 h 15 min
=  5 h 30 min

2. Lewis practised on the piano for 3 h 45 min.
Sebastian practised on the piano for 1 h 35 min.
How much longer did Lewis practice on the piano than Sebastian?

We have to find out,
    3 h 45 min  −  1 h 35 min
=  _____ h ____ min

Step 1: Subtract the minutes.
    45 min  −  35 min
=  10 min

Step 2: Subtract the hours.
    3 h  −  1 h
=  2 h

So,
    3 h 45 min  −  1 h 35 min
=  2 h 10 min

Lewis practised for 2 h 10 min longer than Sebastian.

3. Last week, Rebecca swam for 8 h 25 min while she studied for 6 h 35 min.
How much longer did she spend swimming than studying last week?

We have to find out,
    8 h 25 min  −  6 h 35 min
=  _____ h ____ min

Step 1: Subtract the minutes.
25 min  −  35 min  =  ?
We cannot subtract 35 min from 25 min. So, we regroup 8 h 25 min.

Step 2: Regroup 8 h 25 min.
    8 h 25 min
=  7 h 85 min

Step 3: Subtract.
    8 h 25 min  −  6 h 35 min
=  7 h 85 min  −  6 h 35 min
=  1 h 50 min

She spent 1 h 50 min longer swimming than studying last week.