You could use the work formula and equate both equations

Solution:

Firstly,
time = 3 h
speed = 50 mph
distance = 50 x 3 = 150 miles

Second,
time = 2 h
speed = 40 mph
distance = 40 x 2 = 80 miles

Avg speed = total distance / total time
= 80 + 150 / 2 + 3 = 46

Ans: C

Here, the rate would be
work = 2 pages
time = 3 seconds
rate = work /time = 2/3

Solution:

For 5 hours,
work = 2/3x5x60x60 = 12,000 Ans: C

The problem deals with factors and multiples, so LCM would be the easiest way I feel.

The best way to solve this would be to use the options. Check if the option satisfies both conditions.
Else, start with numbers close to 3 and 5, (1 in this case because it says â€śpositive integersâ€ť) and go on by skipping numbers that are divisible by 3 and 5.
(I think 11 would be the answer)