Numbers - General Questions (4)

The square of a natural number never ends in 7.

42437 is not the square of a natural number.

20 x x = (64 + 36)(64 - 36) = 100 x 28

x =	100 x 28	= 140
	20

4 | x            z = 6 x 1 + 4  = 10
 -----------
 5 | y -2         y = 5 x z + 3  = 5 x 10 + 3  = 53
 -----------
 6 | z - 3        x = 4 x y + 2  = 4 x 53 + 2  = 214
 -----------
   | 1 - 4
   
Hence, required number = 214.

Unit digit in (4137)⁷⁵⁴ = Unit digit in {[(4137)⁴]¹⁸⁸ x (4137)²}

=Unit digit in { 292915317923361 x 17114769 }

= (1 x 9) = 9

Let the two consecutive odd integers be (2n + 1) and (2n + 3). Then,

(2n + 3)² - (2n + 1)² = (2n + 3 + 2n + 1) (2n + 3 - 2n - 1)

     = (4n + 4) x 2

     = 8(n + 1), which is divisible by 8.

80 = 2 x 5 x 8

Since 653xy is divisible by 2 and 5 both, so y = 0.

Now, 653x is divisible by 8, so 13x should be divisible by 8.

This happens when x = 6.

x + y = (6 + 0) = 6.

Let the number be x. Then

	60	x	3	x x = 36
	100		5

x =		36 x	25		= 100
			9

 Required number = 100