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Junior one math topic ~ About fractions ~ ~ ~ ~ ~ ~ Important process, important process, important process, speed, speed, speed ~
Solution 1:

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