Hint: It didn't matter how many male or female borrowers there were.

Answer: 4200 books.

It doesn't matter how many female borrowers there were as 1/2 of the females accepted the books, and those that did accepted 6 books, which is 3 books per female on average.

Similarly it doesn't matter how many male borrowers there were as 3/4 of the males accepted 4 books each, which is again 3 books each.

So both the males and females accepted, on average, 3 books each. And 1400 * 3 = 4200. QED.

Puzzle 999

The International Women's Speed Skating championship was recently completed, however, the computer storing the results suffered from a power cut. Using the following information, can you determine who finished where, their ages (18, 21, 24 and 28) and the colour they wore? The youngest, who didn't wear blue, won the championship. Jessica was three years younger than the person who wore red. Katy performed well to finish in second place. Lauren wore green and Mary was the oldest competitor. The person who wore yellow was younger than Katy, whereas the person who came last was 21.