A researcher who examines the causal relationship between amount of exercise (i. e., participants are randomly assigned to 30 minutes of exercise per day or no exercise) and memory abilities is using the research design.

experimental

Step-by-step explanation:

Experimental research design refers to a research that is conducted with a scientific approach whereby two sets of variables are used. It adheres to the scientific research design.

An experimental research design consist of an hypothesis, a variable which the researcher can manipulate and variables which can be measured. Based on the information given, the experimental research design is used.

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