Question
How many of the following numbers are divisible by 3 but not by 9?
2133, 2343, 3474, 4131, 5286, 5340, 6336, 7347, 8115, 9276
Answer: Option B
- Taking the sum of the digits, we have :
S1 = 9, S2 = 12, S3 = 18, S4 = 9, S5 = 21, S6 = 12, S7 = 18, S8 = 21, S9 = 15, S10 = 24.
Clearly, S2, S3, S6, S8, S9, S10 are all divisible by 3 but not by 9.
So, the number of required numbers = 6
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- Taking the sum of the digits, we have :
S1 = 9, S2 = 12, S3 = 18, S4 = 9, S5 = 21, S6 = 12, S7 = 18, S8 = 21, S9 = 15, S10 = 24.
Clearly, S2, S3, S6, S8, S9, S10 are all divisible by 3 but not by 9.
So, the number of required numbers = 6
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