Subtracted the two clock times directly without accounting for the shift crossing midnight: 10:30 − 6:15 = 4 h 15 min. This ignores the fact that 6:15 a.m. is on the next day.
PRIMARY 4 · MATHEMATICS
Time
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Stopped at 6:00 a.m. and ignored the final 15 minutes. 1 h 30 min (10:30 p.m. to midnight) + 6 h (midnight to 6:00 a.m.) = 7 h 30 min.
Counted 10 p.m. to midnight as a full 2 hours instead of 1 hour 30 minutes (the shift starts at 10:30 p.m., not 10:00 p.m.). 2 h + 6 h 15 min = 8 h 15 min.
Used only 40 minutes for the second leg instead of 1 hour 30 minutes (dropped the 1 hour). 8:15 + 50 min + 20 min + 40 min = 8:15 + 1 h 50 min = 10:05 a.m.
Omitted the 20-minute stopover at Jurong East. Added only the two travel legs: 8:15 + 50 min = 9:05; 9:05 + 1 h 30 min = 10:35 a.m.
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