4 men and 6 women can complete a work in 8 days, while 3 men and 7 women can complete it in 10 days. In how many days will 10 women complete it?

Answer: Option B

Let 1 man's 1 day's work = x and 1 woman's 1 day's work = y
Then, 4x + 6y = $$\frac{1}{8}$$ and 3x + 7y = $$\frac{1}{10}$$
Solving the two equations, we get
$$x=\frac{11}{400},y=\frac{1}{400}$$
∴ 1 woman's 1 day's work = $$\frac{1}{400}$$
⇒ 10 women's 1 day's work = $$\frac{1}{400}\times 10$$   = $$\frac{1}{40}$$
Hence, 10 women will complete the work in 40 days