Question

1. The radioisotope Iodine-123 is used in thyroid therapy. The half-life of this isotope is 13.27 hours.

Answer 1

1. Answer: D. A = 100 (1/2)^t/13.27

Exponent equation formula would be an= a0( 1+r)^t
In this question, the radio isotopes will become half of its weight after the half-life. So, the ratio would be -0.5 (r= -0.5)
The halftime is 13.27 hours, so the time will be divided by that number. The result would look like this:
an= a0( 1+r)^t
an= a0( 1-0.5)^t/13.27
an= a0( 1/2)^t/13.27

2. Answer: x= 74°

The ladder and the building will make a right triangle with the ladder as the hypotenuse. 
The foot of the ladder is 2 feet from the building, so the adjacent side is 2ft.
It reaches a point 7 feet high on the building, so the opposite side is 7ft
You can find the angle by using the tan equation

tan x= opposite / adjacent
tan x= 7/2= 3.5
x= 74°