Is three sixths equivalent to one half?

YES!!!

3/6 = 1/2

NB THree '3' is a common factor of both '3' and '6' , so you cancel down*reduce) by dividing both numbers by '3'

NB You can do this proceedure with any fractions

e.g. 9 /27 = 1/3

16/20 = 4/5

et seq/.