The distance between a and B is 100km, and the driving speed of a car is UKM / h 1) Algebraic expression is used to express the driving time of the car from place a to place B; (2) If the speed is increased by 10km / h, how long does it take to get from place a to place B? How long does it take to get there earlier after the speed is increased? It is expressed in algebraic expressions; (3) When u = 50km / h, calculate the values of the above formulas respectively

The distance between a and B is 100km, and the driving speed of a car is UKM / h 1) Algebraic expression is used to express the driving time of the car from place a to place B; (2) If the speed is increased by 10km / h, how long does it take to get from place a to place B? How long does it take to get there earlier after the speed is increased? It is expressed in algebraic expressions; (3) When u = 50km / h, calculate the values of the above formulas respectively

1.100/U
2.100/(U+10)；100/U-100/（U+10）
3.100/50=2；100/60=5/3；2-5/3=1/3

When a person travels 100km, the speed is 100km / h in the first 60km and 120km / h in the last 40km, what is his average speed?

t1+t2=60/100+40/120=3/5+1/3=14/15
100/(t1+t2)=100*15/14=107

A train from a to B, 5 hours line the whole 4 / 7, according to this speed, a few hours to reach B

5 △ 4 / 7-5 = 15 / 4 = 3.75 hours

A train from a to B, 5 hours of the whole line 4 / 7. The same speed, a few hours to reach B?

Another 15 / 4 hours to reach the second place