Step-by-step answer:
Answer to problems of this kind is the reciprocal of the harmonic mean of the time required.
We need to find the average of the speeds, not the average of the time.
The respective speeds are 1/3 and 1/4.
The average of the speeds is therefore (1/3+1/4)/2 = 7/24 (harmonic mean of the time taken).
The time required is therefore the reciprocal of the unit speed,
T = 1/(7/24) = 24/7 = 3 3/7 minutes, or approximately 3.43 minutes.
I'd start with setting up the equations. Calling x the number of students in most popular country 1, and y in country 2.
x + y = 44740
x - y = 5672
now solve for x1 and x2. You can subtract second from first:
0 + 2y = 39068
y = 19534
so
x = 5672 + 19534 = 25206
Add a sentence to answer it in words.
The slope of a line is always zero because the line does not move up or down on the y-axis.
Let x be the capacity of the tank then
3x/4-x/8 =15,
then x=24, so so far it has 3/4 *24 =18 so you need 6 gallons to fill it up
The answer is 20.
5*10-5*6=50-30=20