Suppose there are x people in the last row and n people in the first row, then from the back

The number of people in the front row is x, kx+ 1, x+2, …, x+

(n- 1).

Because x and n are positive integers and n≥3, n

(n- 1), and the parity of n is different from 2k+(n- 1).

Decomposition of 200 into prime factors indicates that n=5 or n=8. When n=5,

k = 18； When n=8, k=9. * * * There are two different schemes.

2. The formula is (98 ÷ 2-1)+(98 ÷ 4-1) = 71(

answer

First, we know that A and B are positive integers.

Answer? -B? =(a+b)(a-b), and (a+b)(a-b) is an odd number.

Even parity is the same, that is, even or odd. And 2

One big and one small.

(1) If both are odd numbers, then 1 must be excluded because it is odd.

Multiplying this number by 1 is surprising in itself. Then everything else fits.

Among the 98 odd-even cycle numbers, the odd number is 98÷2=49.

(piece), excluding 1, 49- 1=48 (piece)

(2) Both are even numbers, that is, k is even number, and it is two even numbers.

The products are even numbers, so the minimum requirement is that k is a multiple of 4.

But it must be a multiple of 4, 98÷4=24 (pieces) but divided by 4.

The factor of 1 can only be divided by 2×2, which means it cannot be combined.

Same, so 24- 1=23 (pieces)

48+23=7 1 (pieces)