Nancy has 6 pairs of shoes. In fact, 4 fits 3 times into 14, and every time she tallies 4 pair of socks, she buys 2 pairs of shoes. If we number the socks from 1 to 14, we have:
- Socks from 1 to 4 --> 2 pairs of shoes
- Socks from 5 to 8 --> 2 pairs of shoes
- Socks from 9 to 12 --> 2 pairs of shoes
The remaining pair of socks (13 and 14) are not enough to buy any more shoes!