16, 25, 36, 72, 144, 196, 225?

Each of the number except 54, is a multiple of 5.

The pattern is 1², 2², 3², 4², 5², 6², 7² .

But, instead of 5², It is 20, which is to be turned out.

The pattern is 2³, 3³, 4³, 5³, 6³, 7³.

But 100 is not a perfect cube

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

Let the cost price of first bicycle be ? P.
Then, the cost price of second bicycle = ? (1600 - P)

According to the given condition,
[20% of P + 10% of (1600 - P )] - [10% of P + 20% of (1600 - P)] = 5
? [(20P/100) + [10 x (1600 - P)]/100] - [(10P/100) + {20 x (1600 - P)}/100] = 5
? (P/5 + (1600 - P)/10) - (P/10 + (1600 - P)/5) = 5
? P/5 - P/10 + (1600 - P)/10 - (1600 - P)/5 = 5
? 2P = 1600 + 50
? P = 1650/2 = 825
? Cost of second bicycle = (1600 - 825) = ? 775
? Required difference = 825 - 775 = ? 50

Each of the number except 28, is a multiple of 3.

Each of the given number is except 23, is perfect square

Each of the number except 14, is an odd number .

Each of the number except 21, is an even number .

Each of the number except 12, is a prime number