3.4

The number 3.4 is a decimal number and can be written as a fraction by placing it over a power of 10.

3.4 = 34/10

This fraction can be simplified by dividing both the numerator and denominator by their greatest common divisor, which is 2 in this case.

34/10 = 17/5

Therefore, 3.4 can be written as the fraction 17/5.