Channel One" is an educational television network for which participating secondary schools are equipped with TV sets in every classroom. It has been found that 30 30 % of secondary schools subscribe to Channel One, where of these subscribers 15 15 % never use Channel One while 25 25 % claim to use it more than 5 times per week.

1/4 because there is 4 grades.

3+3+3+2*2*2+29*12 = 365

step-by-step explanation:

ending amount = beginning amount / (2^n)

where "n" = number of half-lives (or elapsed time / half-life)

ending amount = 50 mg / (2 ^10 / 5.3)

ending amount = 50 mg / (2 ^ 1.8867924528)

ending amount = 50 m / 3.6981210597

ending amount = 13.5203794557 mg

or about 13.5 mg remain

source:  

there were only 2 presidents that were under the age of 45. theodore roosevelt, and jfk, that makes 5%