A medium question on queues for P2–P4, with a step-by-step solution, diagrams and the answer. Queue questions are already in the Hua Xia Cup's P1 and P2 first rounds, and the P4 papers add square formations.
The question
21 pupils queue in single file for the coach.
Counting from the front, Ming is 9th.
Counting from the back, May is 8th.
May is behind Ming.
How many pupils are between Ming and May?
Show the hints (2)
💡Hint 1: They're counted from different ends. Where is May, counting from the front?
💡Hint 2: 8th from the back means one fewer than 8 stand behind her.
Worked solution
Have a go first, then read the solution step by step.
1.May has 8 − 1 behind her and 21 − 8 = 13 in front, so from the front she is 13 + 1 = 14th.
2.Between them are places 10 to 13: 14 − 9 − 1 = 4.
⚠️Common mistake: putting May at 21 − 8 = 13 from the front, forgetting to add 1.
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