Answer:
Step-by-step explanation:

We know there are 60 minutes in an hour. To find 2/3 of an hour we divide 60/3 to find 1/3 and multiply by 2 so:
60/3 = 20
20*2 = 40 minutes (which is 2/3 of an hour) to do science
We do the same thing with the 40 minutes. To find 1/4 of 40 minutes we divide 40 by 4 and then multiply it by 3 to get 3/4 so:
40/4 = 10
10*3 = 30 minutes
Then subtract the times 40-30 = 10 minutes
It took her 10 more minutes to complete her science homework.
Hope that helps
Length = √area = √81 = 9
diagonal = √2 * side = √2*9 = 9√2
Answer:
0.36427
Step-by-step explanation:
Mean = λ = 18 messages per hour
P(X = x) = (e^-λ)(λ⁻ˣ)/x!
P(X ≤ x) = Σ (e^-λ)(λ⁻ˣ)/x! (Summation From 0 to x)
But the probability required is that the messages thay come in an hour is between 15 and 20, that is, P(15 < X < 20)
P(15 < X < 20) = P(X < 20) - P(X ≤ 15)
These probabilities will be evaluated using a cumulative frequency calculator.
P(X < 20) = 0.65092
P(X ≤ 15) = poissoncdf(18, 15) = 0.28665
P(15 < X < 20) = P(X < 20) - P(X ≤ 15) = 0.65092 - 0.28665 = 0.36427.
You can use the Poisson distribution calculator here
https://stattrek.com/online-calculator/poisson.aspx