Answer: at most 15 pairs of socks
Step-by-step explanation:
Let the number of pair of socks of her sister be , and let the number of pairs Lucy has be
.
Since , Lucy has 4 more than 1/3 the number of pairs of socks as her sister, this means that
.............................. equation 1
Also , Lucy has at most 9 pairs of socks , this means that
....................................... equation 2
Equating the two equations , we have
multiply through by 3
subtract 12 from both sides
Therefore , the sister has at most 15 pairs of socks