### 21. If P(E) = 0.9 and P(F) = 0.8, show that P(EF) ≥ 0.7. In general, prove Bonferroni's inequality, namely, P(EF) ≥ P(E) + P(F) - 1.

21. If P(E) = 0.9 and P(F) = 0.8, show that P(EF) ≥ 0.7. In general, prove Bonferroni's inequality, namely, P(EF) ≥ P(E) + P(F) - 1.