Brenda received 3 times as many grades as Robert. Timothy received half as many 85s as Brenda. How many grades of 85 did Brenda, Robert, and Timothy receive altogether?

The standard deviation would be 6.1947.

Step-by-step explanation:

Since we have given that

Mean = μ = 290

Weight of coffee beans = x = 283 grams

Since P(Z<z)=13% = 0.13

We need to find the standard deviation:

Using the standard normal table,

P(Z<-1.13)=0.13

So, we get that

z = -1.13

Using the z-score formula, we get that

Hence, the standard deviation would be 6.1947.