What is the greatest common factor of 15t and 21?

There is 1 of course ... but 1 doesn't count because were looking for the greatest number so lets try 2 ... no because 2 x? = 15 nothing. so its not 2. lets try 3.

3x5=15 3x7=21. so we have 3 ... lets try 4 ... 4x?=15 ... 4x?=21 ... nothing. lets try 5. we know 5 x 3 = 15 but 5x21 ... nothing. so lets try 6. 6x?=15 ... nothing ... 6x?=21 ... nothing ... lets try 7 ... 7x?=15 ... nothing ... 7x?=21 ... 3 but we are trying to find a same number that can multiply something and get those 2 numbers. so lets try 8 ... 8x?=15 ... nothing 8x?=21 ... nothing ... lets try 9 ... 9x?=15? nothing.

9x?=21 nothing ... lets try 10 ... 10x? = 15 ... nothing we cant do that ... 10x?=21 nothing ... so we have 3 so far that's the greatest common factor ... so your answer is 3