Part C - Elementary Mathematics
If \( \frac{4}{5} \) of A is equal to \( \frac{2}{5} \) of B, find the value of A : B.
A can complete a work in 7 hours, B and C together in \( \frac{21}{4} \) hours, and C and A together in \( \frac{7}{2} \) hours. How long will B alone take to complete the work?
By selling a book at \( \frac{5}{12} \) of the printed price, there is a loss of 50%. What is the ratio of the printed price to the cost price?