Answer:
.
Step-by-step explanation:
Let the unknown fraction be ,
where, x and y both are prime numbers less than 20.
Now, it is given that adding 1 to both numerator and denominator will make the fraction .
Thus,
=
2(x + 1) = y + 1
2x + 2 = y + 1
2x + 1 = y.
Clearly if x will be any odd number , two times x will be odd and adding 1 to it will result in even number and y should be even number , which is not possible as only even prime is 2.
Thus , x should be the even prime which is 2.
And y will be 5.
Thus the required fraction is .