Question

If 1/2 of 5 is 3, then what is 1/3 of 10?

Answer 1

a) If 1/2 of 5 is 3 that means 5/2 = 3 or 5 = 2 x 3
b) ...then what is 1/3 of 10; that means 10/3 or (5x2)/3
But we know from a) that 5 =  2x3. Substitute 5 in b) 

10/3 = (5x2)/10 = (2x2x3)/3 = 4, So 10/3 = 4