1) To solve this expression, we need to follow the order of operations (also known as PEMDAS or BODMAS).

First, we calculate the multiplication and division from left to right:
1997 × 1996 = 3,988,712
995 ÷ 1995 = 0.4987468671679198

Next, we substitute these values back into the expression:
3,988,712 - 0.4987468671679198 × 1997 × 1997

Now, we calculate the remaining multiplication and subtraction:
0.4987468671679198 × 1997 × 1997 = 1,985,000.9999999998
3,988,712 - 1,985,000.9999999998 = 2,003,711.0000000002

Therefore, the solution to the expression is 2,003,711.0000000002.

2) Following the order of operations, we calculate the multiplication and division from left to right:
6001 × 5931 = 35,586,031
5392 × 6001 = 32,356,992

Next, we substitute these values back into the expression:
5392 + 35,586,031 ÷ 32,356,992 - 69

Now, we calculate the remaining addition and subtraction:
35,586,031 ÷ 32,356,992 = 1.0999999999999999
5392 + 1.0999999999999999 - 69 = 5324.099999999999

Therefore, the solution to the expression is 5324.099999999999.

3) To solve this expression, we need to follow the order of operations:

1991 ÷ 1990 = 1.000502512562814
1992 ÷ 1991 = 1.000502512562814
1993 ÷ 1992 = 1.000502512562814
1994 ÷ 1992 = 1.0010050251256281
995 ÷ 997 = 0.9979929775280899

Next, we substitute these values back into the expression:
1.000502512562814 × 1.000502512562814 × 1.000502512562814 × 1.0010050251256281 × 0.9979929775280899

Now, we calculate the remaining multiplication:
1.000502512562814 × 1.000502512562814 × 1.000502512562814 × 1.0010050251256281 × 0.9979929775280899 = 1.0000000000000002

Therefore, the solution to the expression is 1.0000000000000002.