What is the ratio 15 to 35 written as a fraction in lowest term?

The answer is 3 to 7.

In order to reduce a fraction to lowest term, we first must divide both the numerator and denominator by the greatest common divisor.

The greatest common divisor for 15 and 35 is 5:

15 : 35 = (15:5) : (35:5) = 3 : 7