Starting time, finishing time and duration

You can read the twenty-four-hour clock. Today we find starting times, finishing times and durations. Here is today’s question. A puppet show starts at zero eight fifty and lasts twenty-five minutes. At what time does it finish? Use the twenty-four-hour clock. We know the starting time, zero eight fifty. We know the duration, twenty-five minutes. We must find the finishing time. We use a timeline to find it. Each gap is five minutes. We mark the start, zero eight fifty. Five minutes later is zero eight fifty-five. First, count on to the next hour. O’clock times are easy to add to. The next hour is zero nine zero zero. An hour has sixty minutes; we are at fifty. Sixty minus fifty is ten. So we jump ten minutes, to zero nine zero zero. Ten of the twenty-five minutes are used. Twenty-five minus ten is fifteen. Fifteen minutes are still to add. Jump fifteen minutes from zero nine zero zero. Zero nine zero zero plus fifteen minutes is zero nine fifteen. The marks between are zero nine zero-five and zero nine ten. So the puppet show finishes at zero nine fifteen. We found the finishing time. To find the start, work backwards. Start from the finishing time. Jump back fifteen minutes, to zero nine zero zero. Then ten minutes back gives zero eight fifty. A collage session begins at zero nine forty-six and lasts one hour twenty-eight minutes. At what time does it finish? Use the twenty-four-hour clock. Try it first. Pause if you like. Add the one hour first. The hour marks are zero nine zero zero and ten zero zero. Each hour gap is sixty minutes. Zero nine forty-six plus one hour is ten forty-six. We jump one hour, to ten forty-six. Next, count on to eleven zero zero. An hour has sixty minutes; we are at forty-six. Sixty minus forty-six is fourteen. Add fourteen minutes to reach eleven zero zero. Mark eleven zero zero. We jump fourteen minutes, to eleven zero zero. Fourteen of the twenty-eight minutes are used. Twenty-eight minus fourteen is fourteen. Fourteen minutes are still to add. Eleven zero zero plus fourteen minutes is eleven fourteen. Jump fourteen more minutes, to eleven fourteen. The session finishes at eleven fourteen.

A night camera records from twenty-two forty-seven until zero zero twenty-two the next day. Find the recording duration in hours and minutes. Try it first. Pause if you like. The dashed line is midnight. Count on to the next hour first. An hour has sixty minutes; we are at forty-seven. Sixty minus forty-seven is thirteen. Twenty-two forty-seven to twenty-three zero zero is thirteen minutes. We jump thirteen minutes, to twenty-three zero zero. The next hour is midnight, zero zero zero zero. Twenty-three zero zero to zero zero zero zero is one hour. Midnight is zero zero zero zero. Jump one hour to the next day. Then count on to the finish. Midnight to zero zero twenty-two is twenty-two minutes. We jump the last twenty-two minutes. Put the two minute jumps together. Thirteen plus twenty-two is thirty-five. Now add back the one whole hour. The duration is one hour thirty-five minutes. The recording lasts one hour thirty-five minutes. Move forwards for the finish and backwards for the start.