Practicing Success
If A and B are two independent events such that $P(\overline{A} ∩ B)= \frac{2}{15}$ and $ P(A ∩ \overline{B})=\frac{1}{6}$, then P(B), is |
$\frac{1}{5}\, or \, \frac{4}{5}$ $\frac{1}{6}\, or \, \frac{5}{6}$ $\frac{4}{5}\, or \, \frac{1}{6}$ $\frac{5}{6}\, or \, \frac{1}{5}$ |
$\frac{4}{5}\, or \, \frac{1}{6}$ |
Let P(A) = x and P(B) =y. Since A and B are independent events. Therefore, $P(\overline{A} ∩ B)=\frac{2}{15}$ $⇒ P(\overline{A})P(B)=\frac{2}{15}$ $⇒ \begin{Bmatrix} 1-P(A)\end{Bmatrix} P(B)= \frac{2}{15}$ $⇒ (1-x)y=\frac{2}{15}$ $⇒ y - xy = \frac{2}{15}$ ...........(i) and, $P(A ∩ \overline{B})=\frac{1}{6}$ $⇒ P(A) P(\overline{B})=\frac{1}{6}$ $⇒ x(1-y)=\frac{1}{6}⇒x-xy=\frac{1}{6}$ ..............(ii) Subtracting (i) from (ii), we get $x-y = \frac{1}{30}⇒ x =\frac{1}{30}+y$ Putting this value of x in (i), we get $y-y\left(\frac{1}{30}+y\right)=\frac{2}{15}$ $⇒ 30y - y - 30 y^2 = 4$ $⇒ 30y^2 -29y + 4= 0$ $ ⇒ (6y -1) (5y-4) = 0 ⇒ y=\frac{1}{6} $ or, $ y =\frac{4}{5}$ $∴ P(B)=\frac{1}{6} $ or, $ P(B)=\frac{4}{5}$ |