The following table summarizes 204 endothermic reactions involving sodium bicarbonate.
Let A denote the event that a reaction’s final temperature is 271 K or less. Let B denote the event that the heat absorbed is below target. Determine the number of reactions in each of the following events.
Step 1 of 6:
The data regarding the summaries of 204 endothermic reactions is given.
Final Temperature conditions 
Heat absorbed (cal) 

Below target 
Above target 

266K 
12 
40 
271K 
44 
16 
274K 
56 
36 
Also, it is given that A denotes the event that a reaction's final temperature is 271K or less and B denotes the event that heat absorbed is below target.
Using this we need to find the required values.
Step 2 of 6:
(a)
Here we have to determine the number of reactions corresponding to event AB.
A=Reaction’s final temperature is 271K or less.
So
A={12,40,44,16}
B=Heat absorbed is below target
So
B{12,44,56}
Hence AB={12,44}.
Then the number of reactions in this event become 44+12=56 reactions.
Thus, the number of reactions in the event AB is 56 reactions.
Step 3 of 6:
(b)
Here we have to determine the number of reactions in the event
denotes the event that the reaction’s final temperature is more than 271K.
So, the number of reactions in the set become 56+36=92 reactions.
Thus, the number of reactions in the event are 92 reactions.