It is 4/21
21/12 as a reduced fraction = 1.75
Reduced to its most simplified form, 21 over 12 (or 7/4) is "one and three-quarters" 13/4
12/21 = 4/7
By dividing both the numerator and denominator by 3, 12/21 can be cancelled down to 4/7, or four sevenths.
13/21 can't be reduced.
21/40 cannot be reduced.
25/21 is already reduced to its lowest terms
736 and 21 are comprime so the fraction cannot be reduced.
The fraction 19/21 cannot be reduced any more.
No.
Yes, 21/3 = 7/1