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Practice Questions on Number System

Q25) Find the smallest 6 digit number that is divisible by 13?
1) 100001
2) 99996
3) 100009
4) 999995
Divide 99999(Largest 4 digit number) by 13 and get remainder 'R'.
R = 3.
∴ Largest 4 digit number divisible by 13 is (99999 - R) = (99999 - 3) = 99996
Required number = 99996 + 13 = 100009
Hence, Option 3.


Q26) Which of the following pairs contains a number that is not an integer?
1) (a/b, b/e)
2) (c/e, a/d)
3) (de/6, a/d)
4) (c/b, a/4)
a = 4b = 6c = 9d = 12e
Hence, option 4.


Q27) If c is a positive integer and (c + 1)(c + 3) is odd, then (c + 2)(c + 4) must be a divisible by which one of the following?
1) 16
2) 6
3) 3
4) 8
As (c + 1)(c + 3) is odd, so c + 1 and c + 3 must be odd. This, is possible only when c is even.
Therefore, c = 2d , where d is a positive integer.
(c + 2)(c + 4) = (2d + 2)(2d + 4) = 4(d + 1)(d + 2)
Here, either d + 1 is even or d + 2 is even. So, (c + 2)(c + 4) must be divisible by 8.
Hence, option 4.


Q28) It is given that (224 + 1) is completely divisible by N. Which of the following numbers is completely divisible by N?
1) (212 - 1)
2) (236 - 1)
3) (248 - 1)
4) (272 - 1)
(224 + 1) = y + 1 where y = 224
(248 - 1) = (y2 - 1) = (y + 1)(y - 1)
Hence, option 3.









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