Unit 3 · Measurement and Data
Digital Clock — Add Hours and Minutes
Lesson 1 of 12
Let's start with one of the most reliably scorable question types in OC MR Measurement: adding a large number of minutes to a given time. The trick is that students who try to count minute-by-minute lose time and make errors — students who know the two-step conversion breeze through.
Time-addition problems appear in virtually every OC MR paper, usually in the first half of the test. They are worth securing early — a confident solve here frees up time for harder questions later.
The examiner is checking whether you can convert a raw minute count into hours and leftover minutes, add the hours to the start time (handling midnight or noon crossings), and then add the remaining minutes — without confusing am and pm.
A start time is given in 12-hour format (e.g. 10:25 pm). A large number of minutes is added — often 200–600 minutes, enough to cross midnight. You must give the final time in 12-hour format, including the correct am/pm.
Best approach: Step 1: Divide the minutes by 60. The quotient is the hours to add; the remainder is the leftover minutes. Step 2: Add the hours to the start time, flipping am/pm if you cross midnight or noon. Step 3: Add the leftover minutes, carrying into the next hour if needed. Always state am or pm in your answer.
Question
A digital clock shows 10:25 pm.
What time will it show 400 minutes later?
Select an answer to see the explanation.
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