To write a percent as a fraction in lowest terms, first remember that a percent is a ratio that compares a number to 100. 45% can be written as the ratio 45 to 100 or 45/100. Notice however that 45/100 is not in lowest terms so we need to dive both the numerator and denominator by the greatest common factor of 45 and 100 which is 5.
45 ÷ 5 = 9
100 ÷ 5 = 20
Therefore, 45% can be written as the fraction 9/20.