9. Satisfied Pikes. 40 pikes were released into the pond. A pike is satisfied if it has eaten three other pikes (satisfied or hungry). What is the maximum number of pikes that can be satisfied?
9. We will feed the pikes in three stages. Initially, we will feed 9 pikes, after which there will be 9 full and 4 hungry pikes left. Then, with the nine full pikes, we will feed three hungry pikes, and with three "newly" full pikes, we will feed the last hungry pike. In total, 13 pikes have been fed. Note that as each new full pike appears,

How best? 78

the total number decreases by 3, so we cannot feed more than 13 pikes.