Answer (all) will mark 1) if a plane is flying at 40 mph while another plane is flying at 100 mph and they are 200 miles apart, how long will it take them to collide? 2) ivan and kate live 40 miles apart. if ivan started pedaling towards kate at 8: 00 a. m. at a steady 12 mph while kate left to meet ivan at 9: 30 a. m. but rode at 16 mph, at what time will they meet? 3) a truck with a heavy load drove from boston to new york at 40 mph. after unloading, it returned from new york to boston at a speed of 60 mph. what was its average speed for the whole trip?

1) If a plane is flying at 40 mph while another plane is flying at 100 mph and they are 200 miles apart, how long will it take them to collide?
time=distance/speed
distance between the planes=200 miles
relative speed=(100+40)=140 mph
thus time taken for them to collide will be:
200/140
=1.43 hours

2] Ivan and Kate live 40 miles apart. If Ivan started pedaling towards Kate at 8:00 a.m. at a steady 12 mph while Kate left to meet Ivan at 9:30 a.m. but rode at 16 mph, at what time will they meet?
Time=(distance)/(speed)
relative speed=(40+12)=52 mph
distance=40 miles
thus
time=40/52=0.769 h=0.8 hours=48 min
time they will meet will be:
9:30+48=10:18 a.m

3) A truck with a heavy load drove from Boston to New York at 40 mph. After unloading, it returned from New York to Boston at a speed of 60 mph. What was its average speed for the whole trip?

average speed is given by:
(40+60)/2
=100/2
=50 mph