Question

80 bulbs are selected at random from a lot and their life time ( in hours) is recorded in the form of a frequency table given below:

$\begin{array}{cccccc}Lifetime\left(inhours\right)& 300& 500& 700& 900& 1100\\ Frequency& 10& 12& 23& 25& 10\end{array}$

One bulb is selected at random from the lot. The probability that its life is 1150 h, is:

A) $\frac{1}{80}$
B) $\frac{7}{16}$
C) 0
D) ​​​​​​​1​​​​​​​

Answer 1

The answer is C.
Number of bulbs in the lot, n(S) = 80
Number of bulbs whose lifetime is 1150, n(E) = 0
$\therefore$ Probability that its lifetime is 1150 h $=\frac{n\left(E\right)}{n\left(S\right)}=\frac{0}{80}=0$.
Hence, the probability that its lifetime is 1150 is 0.