Answer:
The probability that at least 1 car arrives during the call is 0.9306
Step-by-step explanation:
Cars arriving according to Poisson process - 80 Cars per hour
If the attendant makes a 2 minute phone call, then effective λ = 80/60 * 2 = 2.66666667 = 2.67 X ≅ Poisson (λ = 2.67)
Now, we find the probability: P(X≥1)
P(X≥1) = 1 - p(x < 1)
P(X≥1) = 1 - p(x=0)
P(X≥1) = 1 - [ (e^-λ) * λ^0] / 0!
P(X≥1) = 1 - e^-2.67
P(X≥1) = 1 - 0.06945
P(X≥1) = 0.93055
P(X≥1) = 0.9306
Thus, the probability that at least 1 car arrives during the call is 0.9306.
The number ... n
one quarter of the number ... 1/4 of n = 1/4 * n
one third of the number ... 1/3 of n = 1/3 * n
one quarter of the number is subtracted from one third of the number ... 1/3 * n - 1/4 * n
the result is 7 ... = 7
We can put it together:
1/3 * n - 1/4 * n = 7
4/12 * n - 3/12 * n = 7
1/12 * n = 7 /*12
n = 7 * 12
n = 84
The number you are looking for is 84.