P (A union B)

Archive SAT Subject Test Preparation
1

<p>A coin is tossed three times. Let A = {three heads occur} and B = {at least one head occurs}. What is P (A union B)?</p>

<p>I thought it was P(A) + P(B) - P(A*B)</p>

<p>So (1/8) + (7/8) - (7/64).</p>

<p>But hte answer is (7/8). Where am I going wrong?</p>