Answer: 9990
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Explanation:
Start with the largest four digit number possible (9999) and see if it's divisible by 3, 6 and 9
- 9999/3 = 3333
- 9999/6 = 1666.5
- 9999/9 = 1111
When dividing the number over 6, we don't get a whole number. So 6 is not a factor of 9999, and we cross 9999 off the list.
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Decrease the number by 9. We do this because the result will be another multiple of 9 (which is automatically also a multiple of 3 as well, since 9 = 3*3)
So we go from 9999 to 9990
Repeat the last set of steps we did earlier
- 9990/3 = 3330
- 9990/6 = 1665
- 9990/9 = 1110
Every result is a whole number, which shows that 9990 is a multiple of 3, 6 and 9. In other words, 9990 is divisible by 3, 6 and 9. It's the largest such 4 digit number.
