Which is not a factor of 72? 1,9,24,144

first you need to know what a factor is > a factor is a whole number that fits to another whole number

lets try 72

72/1 = 72

72/9 = 8

72/24 = 3

72/144 = 0.5

the all fit perfectly except for 144

summary

a factor is a number when divided or multiplied by another number the result is an integer

144 cannot be a factor of 72 since it is bigger than 72