Question 7
Back to Exercise
How many 3-digit numbers have digits that add up to 5?
- A 21
- B 15 Correct
- C 10
- D 12
Correct Answer: Option B
a + b + c = 5 with a ≥ 1 → a′ + b + c = 4
(4 + 2)C2 = 15
Trap: 21 lets the first digit be 0.
Answer: 15
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