A pharmacologist measured the concentration of dopamine in the brains of several rats. The mean concentration was 1,269 ng/gm and the standard deviation was 145 ng/gm.4 What was the standard error of the mean if:.(a) 8 rats were measured? (b) 30 rats were measured?

51.265242 ng/gm ; 26.473257 ng/gm

Step-by-step explanation:

The standard error of the mean = standard deviation / √sample size

Given that:

mean concentration = 1,269 ng/gm

Standard deviation (s) = 145 ng/gm

Standard Error if 8 rats were measured :

Sample size (n) = 8

Standard Error = s / √n

Standard Error = 145 / √8

Standard Error = 145 / 2.8284271

Standard Error = 51.265242 ng/gm

If 30 rats were measured :

Standard Error = 145 / √30

Standard Error = 145 / 5.4772255

Standard Error = 26.473257 ng/gm

n=9

step-by-step explanation:

7 times a number = 7n

decreased by 13 = 7n-13

same as is =

5 times the number = 5n

increased by 5 = 5n+5

7n-13 = 5n+5

2n=18

n=9

the solution of the equation is 2.23 ⇒ answer b

step-by-step explanation:

* lets revise the meaning of exponential function

- the form of the exponential function is y = ab^x, where a ≠ 0, b > 0 ,  

  b ≠ 1, and x is any real number

- it has a constant base b

- it has a variable exponent x

- to solve an exponential equation, take the log or ln of both sides,  

  and solve for the variable

* lets solve the problem

∵

- the base is 7 and the exponent is x

- insert ㏑ in both sides

∴

- use the rule

∴ x ㏑(7) = ㏑(77)

- to find x divide both sides by ㏑(7)

∴

* the solution of the equation is 2.23 to the nearest 2 decimal places