Two cities are 45 miles apart. two trains, with speeds of 70 mph and 60 mph, leave the two cities at the same time so that one is catching up to the other. how long after the trains leave will the distance between them be 10 miles? a how many solutions does the problem have?

The correct answer is  27' (minutes). The problem actually has only one solution.

Explanation:

s=d/t

70=d1/t

70t = d1

60=d2/t

60t = d2

d1 + d2 + 10 = 45

70t + 60t = 35

130t = 35

t=27’

The problem actually has only one solution.

two jet streams that directly affect the formation of weather in the continental part are a polar jet and a subtropical jet. they are responsible for the transportation of weather systems, which directly affect people. the polar front is the boundary between cold air from the north pole and warmer equatorial air. both the polar jet and the subtropical jet blow from the west to the east, and follow the boundary between cold and warm air.

the strongest jet streams are polar jets, while subtropical jets are somewhat weaker.

the right answer is c. the polar jet stream is generaly stronger than the subtropical jet stream.