A) 72 (7!)
B) 18 (7!)
C) 40 (7!)
D) 36 (7!)
Correct Answer: D
Solution :
We know that any number is divisible by 9 if sum of the digits of the number is divisible by 9. Now sum of the digits from 0 to 9 = 0 + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = 45 Hence to form 8 digits numbers which are divisible by 9, a pair of digits either 0 and 9, 1 and 8, 2 and 7, 3 and 6 or 4 and 5 are not used.Digits which are not used to form 8 digits number divisible by | Number of 8 digits numbers which are divisible by9 |
0 and 9 | \[8\times 7!\] |
1 and 8 | \[7\times 7!\] |
2 and 7 | \[7\times 7!\] |
3 and 6 | \[7\times 7!\] |
4 and 5 | \[7\times 7!\] |
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