331, 482, 551, 263, 383, 362, 284

Each of the numbers except 72 is a perfect square.

Each of the numbers except 21 is an even number.

(1*1)+1 , (2*2)+1 , (3*3)+1 , (4*4)+1 , (5*5)+1 , (6*6)+1 , (7*7)+1 , (8*8)+1

But, 64 is out of pattern.

The pattern is 1 ², 2 ², 3 ², 4 ², 5 ², 6 ², 7 ². But, instead of 5 ², it is 20 which to be turned out.

Each of the numbers except 23, is perfect square.

In each number except 751, the difference of third and first digit is the middle one.

Each of the numbers except 81 is a prime number.

Each of the numbers is a prime number except 12.

Let the speed of two trains be 7x and 8x km/hr.

Then, 8x =	❨	400	❩	= 100
		4

⟹ x =	❨	100	❩	= 12.5
		8

∴ Speed of first train = (7 x 12.5) km/hr = 87.5 km/hr.

(1/2)x	+	(1/2)x	= 10
21		24

⟹	x	+	x	= 20
	21		24

⟹ 15x = 168 x 20

⟹ x =	❨	168 x 20	❩	= 224 km.
		15