Two cars and one * * * line 4/7+3/5 = (20+21)/35 = 41/35.

Distance =120/(41/35-1) =120/(6/35) = 700 (secretion? )

2) The difference between denominator and numerator is constant =89-44=45.

The denominator is 7/2 times that of the numerator, and the difference is multiple.

Molecule =45/(7/2- 1)= 18

The number subtracted is 44- 18=26.

3) Two-car speed 15km/h, four-hour speed 15 * 2 * 4 = 120km.

The sum of the speeds of two vehicles =120km/h.

Distance = 120 * 5 = 600km.

4) The speed of B is 7/ 10 of A, and when A is 3/7, B is 3/7*7/ 10=3/ 10.

Distance = 36/(3/ 10) = 120km.

12) A+B = 1/7, and 5/7 was completed after 5 days of cooperation.

( 1- 1/5)B =( 1-5/7)/6 = 1/2 1。

b = 1/2 1/( 1- 1/5)= 5/84。

a = 1/7-5/84 = 7/84 = 1/ 12。

A it takes 12 days to complete it alone.