If both A and B are expanded to five times, the score is:

5a×5b/(5a+5b)

=25ab/[5(a+b)]

=5ab/(a+b)

The value of the score is five times that of the original.

Solution 2: 20 minutes = 1/3 hours, the original speed is a/b km/ hour, the time to arrive 20 minutes earlier is (b- 1/3) hours, and the speed to arrive 20 minutes earlier is a/(b- 1/3)km/ hour.

A/(b-1/3)-a/b = 3a/(3b-1)-a/b (km/h)

Xiaoming walks [3a/(3b- 1)-a/b] kilometers every hour.

Solution 3: Let x/2=y/3=k, then x=2k and y=3k.

(7x？ -Really? )/(x？ -2xy+3y？ )

=[7×(2k)？ -(3k)？ ]/[(2k)？ -2×2k×3k+3×(3k)？ ]

=(7×4k？ -9k？ )/(4k？ - 12k？ +3×9k？ )

=(28k？ -9k？ )/(4k？ - 12k？ +27k？ )

= 19k？ / 19k？

= 1