Chance

#1
I am not exactly sure of the correct statistical method to execute this problem"

A fair coin was flipped 10 times, compute the chance that the number of heads is less than 4.

Now does this require the use of the complementary rule: "the chance the thing will happen equals one minus the chance that the thing will not happen"?

I would know how to answer this question if it asked for the chance that the number of heads is at least 4, but I am not sure how to do it for this problem.
 
#3
Let H be the event of acquiring a head by flipping a coin

the chance that the number of heads is less than 4 is:
P(H < 4) = 1 - P(H >= 4) >>> used the complementary rule that you are saying

now you can answer the problem since you said that you know what to do when the question asked is about the chance that the number of heads is at least 4 [P(H >= 4)]

:D