Mary starts from her house, walks 80 meters south, and stops to chat with her aunt on the sidewalk. after chatting for a few minutes, she walks 125 meters to the west to meet a friend and then walks 45 meters north with her friend to a cafe for lunch. overall, she takes 10 minutes to do all this. what is mary’s average speed?
a. 8 meters/second
b. 1.25 meters/second
c. 25 meters/second
d. 4.5 meters/second
e. 0.42 meters/second

E. 0.42 meters / second

Since you are finding the average speed, you don't need to factor in all the stops Mary makes on her way to her final destination. Add the total distance she walked ( 80 + 125 + 45 ) and divide it by the amount of time IN SECONDS that it took for her to do this. Since the time given is in minutes, simply multiply the number of minutes ( 10 ) by 60 ( the amount of seconds in a minute ). Then divide the total number of meters walked by the total amount of seconds it took to walk, and you will get your average speed.

( Also, this is a Physics question, not Chemistry :D )

They are all decomposition reactions.