Answer:
D. 12/7
Step-by-step explanation:
The first thing is to define the variables of each one,
Let W be the rate for a woman
Let M be the rate for a man
Let G be the rate for a girl
According to the statement, we have to:
W + M = 1/2
W + 2 * G = 1/2
M + G = 1/4
Now if we add all the previous equations:
2 * W + 2 * M + 3 * G = 5/4
We have that there is a common factor 2
2 * (W + M + (3/2) * G) = 5/4
In the end we have:
W + M + 1.5 * G = 5/8
From which we can lower the following:
Time required would be the inverse of the equation, that is:
1 / W + 1 / M + (2/3) * G = 8/5
Therefore 8/5 = 1.6
BUT we need 1G and we have more 0.5G. Which implies that the time will be little more than 1.6.
If we check the answers
Options A, B, C are less than 1.6. Delete them.
Option E is more than 2 hours. It is an exaggerated time, since it is only 0.5 more time and should logically be less than 2 hours when all of them combined work together. Delete E
The only answer that remains, would be the correct one, that is, D 12/7, which is a little greater than 1.6.
