<p>Almost correct, except P(MA) = 1 - (1-p)^3 .</p>
<p>Also, the phrase ‘…breaks down 20% more than machine B’ is a bit ambiguous. The way you construed it is probably correct i.e.
1 -(1-p)^3 = 0.2 + p^3 ----------------- (1)</p>
<p>but (IMO), someone could also read it as
1 - (1-p)^3 = 1.2 (p^3) ----------------- (2)</p>
<p>However, eq.(2) leaves you with a cubic equation to solve for p, whereas eq. (1) leaves you with a quadratic. (2) is unlikely - go with (1). If you expand both sides fully, the p^3 will cancel on both sides, leaving you with a quadratic equation in p.</p>