The denominator is the bottom number.
To change the 5 to 10, you would multiply 5 by 2: 5 x 2 = 10
Because you multiplied the 5 by 2, you also need to multiply the numerator ( top number) by the same amount.
1 x 2 = 2
So 1/5 = 2/10
The answer is 2/10