1, a proportional formula, the sum of the two external terms is 37, the difference is 13, and the ratio is 12/25. Write this proportional formula.

x+y=37

x-y= 13

x=25，y= 12

The ratio formula is 12:25= 12:25.

2. The ratio of ...................................... ■ The two ratios are 12/5. Write this proportional formula.

24/ 10=36/ 15

3. The construction of a highway was originally planned to be completed in 12 days, with 40 participants. Due to the increase of workers, it was completed two days ahead of schedule. How many workers have been added? (Answer in the way of solution)

Suppose x workers are added.

(40+x):12 = 40: (12-2) ............... is inversely proportional.

400+ 10X=480

X=8