Tommy was walking at a rate of 4 miles hour at noon and at 12: 30 pm he was walking at a brisk rate of 6 miles hour . two hours later tommy was walking at a leisurely rate of 2 miles hour . which statement about tommy's accleration is true? a) tommy had an accleration of zero the entire time. b) tommy had a positive acceleration between noon and 12: 30 pm. c) tommy had a positive acceleration between 12: 30 and 2: 30 pm. d) tommy had a negative acceleration between noon and 12: 30 pm.

A positive acceleration indicates that the object sped up. This means that if you compare the first speed to the second, the second speed should be higher. 

A negative acceleration indicates that the object has slowed down. This means that if you compare the first speed to the second, the second speed should be lower.

If an acceleration is 0, it means that it neither slowed down nor sped up.

Now let us analyze your problem by listing down the speed and the time:

At noon: 4 mi/hr 
12:30 :   6 mi/hr
2:30   :   2 mi/hr

From noon to 12:30, you will notice that there is an increase in speed. This means that Tommy had a positive acceleration. (Rules out D.)

From 12:30 to 2:30, there is a decrease in speed. This would indicate that Tommy had a negative acceleration. (Rules out C.) 

No speed was the same, so acceleration was never 0. (Rules out A.)

From the assumptions above, we can now deduce that the answer is B.