A medium question on clocks and time for P3–P4, with a step-by-step solution, diagrams and the answer. Every year of the Hua Xia Cup has clock questions, from time passed in P1 to the angle between the hands in P6.
The question
The big clock in a shopping centre strikes the hours:
3 times at 3 o'clock, 4 times at 4 o'clock, and so on, with the same gap between one strike and the next.
At 4 o'clock there are 6 seconds between the first strike and the last.
At 12 o'clock, how many seconds are there between the first strike and the last?
Show the hints (2)
💡Hint 1: At 4 o'clock there are 4 strikes. How many gaps are there between them?
💡Hint 2: First find how many seconds each gap lasts.
Worked solution
Have a go first, then read the solution step by step.
1.4 strikes have 4 − 1 = 3 gaps between them: each is 6 ÷ 3 = 2 seconds.
2.12 strikes have 11 gaps: 2 × 11 = 22 seconds.
⚠️Common mistake: working out 6 ÷ 4 for each gap, forgetting that 4 strikes have only 3 gaps.
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