Solution:

To find the probability of obtaining not more than 3 heads, we need to first find the probability of obtaining 0, 1, 2, or 3 heads in a single toss of the coin.

Probability of getting heads in a single toss = 1/2

Probability of getting tails in a single toss = 1/2

To find the probability of obtaining 0 heads, we need to toss the coin 0 times. The probability of getting tails every time is (1/2)0 = 1.

To find the probability of obtaining 1 head, we need to toss the coin 1 time. The probability of getting heads is 1/2 and the probability of getting tails is also 1/2. So, the probability of obtaining 1 head is 1/2.

To find the probability of obtaining 2 heads, we need to toss the coin 2 times. There are two possible outcomes: HH and HT. The probability of getting HH is (1/2) x (1/2) = 1/4 and the probability of getting HT is (1/2) x (1/2) = 1/4. So, the probability of obtaining 2 heads is 1/4 + 1/4 = 1/2.

To find the probability of obtaining 3 heads, we need to toss the coin 3 times. There are three possible outcomes: HHH, HHT, and HTT. The probability of getting HHH is (1/2) x (1/2) x (1/2) = 1/8, the probability of getting HHT is (1/2) x (1/2) x (1/2) = 1/8, and the probability of getting HTT is (1/2) x (1/2) x (1/2) = 1/8. So, the probability of obtaining 3 heads is 1/8 + 1/8 + 1/8 = 3/8.

Therefore, the probability of obtaining not more than 3 heads is the sum of the probabilities of obtaining 0, 1, 2, or 3 heads, which is:

1 + 1/2 + 1/2 + 3/8 = 7/8

So, the answer is A. 3/4.

D