The sum of the numerator and denominator of a fraction is 21. After the denominator is increased by 19, you can get the simplest fraction 1 / 4, and find the original number. Hurry, I have to hand it in this afternoon. Who will say it quickly

The sum of the numerator and denominator of a fraction is 21. After the denominator is increased by 19, you can get the simplest fraction 1 / 4, and find the original number. Hurry, I have to hand it in this afternoon. Who will say it quickly

Molecule = (21 + 19) / (1 + 4) = 8
Denominator = 21-8 = 13
Original = 8 / 13