Question

A box contains four 40-W bulbs, five 60-W

Answer 1

So first one is not a 75W bulb:

P(not a 75Wbulb)=(4+5)/(4+5+6)=9/15

P(a 75W bulb)=6/(15-1)=6/14

9/15*6/14=9/35

Answer 2

Answer: 0.99483

Step-by-step explanation:

Given : A box contains four 40-W bulbs, five 60-W  bulbs, and six 75-W bulbs.

Total bulbs : 4+5+6=15

The probability of selecting a 75-W bulb :$p=\dfrac{6}{15}=0.4$

Using the binomial probability :-

$P(X)= ^nC_xp^x(1-p)^{n-x}$, where P(x) is the probability of getting success in x trials , p is the probability of getting success in each trial and n is the total number of trials.

We have,

The  probability that at least two bulbs must be  selected to obtain one that is rated 75W :-

$P(x\geq2)=1-(P(x$

Hence, the required probability = 0.99483