a2zinterviews

16.	The digit in unit's place of the product 81 ×82×.....×89 is
	A.  0
	B.   2
	C.  6
	D.  8

Solution

Required digit = Unit digit =(1×2×3×4×5×6×7×8×9) =0.

17.	What leat value must be assigned to * so that the number 63576*2 is divisible by 8?
	A.  1
	B.  2
	C.  3
	D.  4

Solution

The given number is divisible by 8, if the number 6x2 is divisible by 8. Clearly, the least value of x is 3.

18.	The sum of first 45 natural numbers is
	A.  1035
	B.  1280
	C.  2070
	D.  2140

Solution

We know that(1+2+3+.....+45) = n(n+1)/2 Therefore (1+2+3+....+45) =(45×46 / 2) = 1035.

19.	The sum of even numbers between 1 and 31 is
	A.  16
	B.  128
	C.  240
	D.  512

Solution

Required numbers are 2, 4, 6,..30. This is an A.P containing 15 terms. Required sum = n/2(first term + last term) ‹=›15 / 2(2+30) ‹=› 240.

20.	How many numbers between 200 and 600 are divisible by 4,5 and 6?
	A.  5
	B.  6
	C.  7
	D.  8

Solution

Every such number must be divisible by L.C.M of 4,5,6 i.e, 60. Such numbers are 240,300,360,420,480,540. Clearly, there are 6 such numbers.