Advanced Mathematics Primary 4 Whole Numbers

Mei Ling thinks of a 4-digit number. When rounded to the nearest thousand, it becomes 6 000. When rounded to the nearest hundred, it becomes 5 900. When rounded to the nearest ten, it becomes 5 890. What is the smallest possible number she could be thinking of?

A 5 850
B 5 885
C 5 895
D 5 900
Show Worked Solution

Worked Solution

Step 1: Find numbers that round to 6 000 (nearest thousand). Range: 5 500 to 6 499. Step 2: Find numbers that round to 5 900 (nearest hundred). Range: 5 850 to 5 949. Step 3: Find numbers that round to 5 890 (nearest ten). Range: 5 885 to 5 894. Step 4: Find the intersection of all three ranges. All three: 5 885 to 5 894. Step 5: The smallest number in this intersection is 5 885. Verify 5 885: Nearest ten: units digit 5 ≥ 5, round up → 5 890 ✓ Nearest hundred: tens digit 8 ≥ 5, round up → 5 900 ✓ Nearest thousand: hundreds digit 9 ≥ 5, round up → 6 000 ✓ Answer: 5 885

Correct answer: 5 885

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