Directly proportional or positively correlated
A. 11/30 x 50= 18/36=1/2
18/36 x 1/10= 5/100
B. 1,210 x 1.1= 1,331
I am not so sure about A, but I hope this helps a little.
ANSWER
The radius is 25 inches
EXPLANATION
From the diagram, the radius of the circle is AC.
From the Pythagoras Theorem,


Simplify

Take positive square root,


Hence the radius is 25 inches
If he paid $57 monthly for 14 months, the total amount paid is:

He paid $798 in total
No this is not a valid reference because those were 20 random families, if he does another test the next twenty families 50% of them could attend the party. Too much chance to be valid.