What is ones digit of the product when twenty 3's are multiplied?
Note the pattern for n ≥ 0....where n is an integer
3^[1+ 4n] ends in 3
3^[2 + 4n] ends in 9
3^[3 + 4n] ends in 7
3^[4 + 4n] ends in 1
So
3^20 = 3^[4 + 4*4] ends in 1
