C. 60: 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, and 60
1,000: 1, 2, 4, 5, 8, 10, 20, 25, 40, 50, 100, 125, 200, 250, 500, 1000
Now we find the common numbers. One doesn’t count as when multiplied later on, it will not change anything.
60: 2, 4, 5, 10, 20
1,000: 2, 4, 5, 10, 20
The highest common factor is 20 because it’s, well, the highest number.
D. Do the same thing for D.
24: 1, 2, 3, 4, 6, 8, 12, 24
880: 1, 2, 4, 5, 8, 10, 11, 16, 20, 22, 40, 44, 55, 80, 88, 110, 176, 220, 440, 880
20 and 880: 2, 4, 8
8 is the Highest Common Factor.
E. Do the same thing with E.
90: 1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45, 90
1,000: 1, 2, 4, 5, 8, 10, 20, 25, 40, 50, 100, 125, 200, 250, 500, 1000
90 and 1000: 2, 5, 10
10 is the Highest Common Factor.
The correct answer is C. So, lets go first to the equations that determine the volume of these solids. For the cylinder, that is simple; pi*r*r*h where r is the radius, h is the height and pi is the constant 3.14. For the cone, it is not easy to derive but one gets that the formula is:

.
We notice thus that

. That holds irrespective of their radius or height; we only need to know that the heights and radii of the two objects are the same. Now, we have thus that:

.
We can check if this holds for Jared's statement; 1178/4712=0.25=1/4. So, it does not hold and thus Jared's statement is incorrect.