How can the crossing be safely made?

Question

I am stumbed assisting my son with this math problem:

Three missionaries and three cannibals wish to cross a river using a single boat that will hold only two people. If at any time the cannibals outnumber the missionaries, those missionaries will be eaten. How can the crossing be safely made?

Answer 1

i will denote the river by a double bar

MMMCCC ||
MMMC || CC

return one C
MMMCC || C
MMM || CCC

return one C
MMMC || CC
MC || MMCC

return one M and one C
MMCC || MC
CC || MMMC

CCC || MMM ... by this time the missionaries are safe... the cannibals can collect the rest...
C|| CCMMM
CC || CMMM
|| CCCMMM


§

Answer 2

One missionary and one cannibal row across.
Balance 2:2 on shore; 1:1 in boat
Leave the cannibal and missionary rows back alone
Balance 2:2 on 1st shore; 1:0 in boat; 0:1 on 2d shore
Two cannibals row across
Balance 3:0; 0:2; 0:1
Leave one cannibal and return
Balance 3:0; 0:1: 0:2
Two missionaries row across
Balance 1:1; 2:0; 0:2
Leave one missionary and pick up one cannibal
Balance 1:1; 1:1; 1:1
Drop cannibal on original shore and pick up remaining missionary
Balance 0:2; 2:0; 1:1
Both missionaries stay on 2d shore
Balance 0:2; 0:0; 3:1
In two trips a cannibal rows across and pick up each of the other two cannibals
Final balance 0:0; 0:0; 3:3