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Permutations Practice Test 2
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© examsnet.com
Question : 20
Total: 30
How many 10 digits numbers can be written by using the digits 1 and 2?
10
C
1
+
9
C
2
2
10
10
C
2
10!
Validate
Solution:
Since each place of 10 digit number can be filled by 2 digits in two ways.
∴ Required number
=
2
10
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