Yes, 4/5 is a rational number. A rational number is defined as any number that can be expressed as the quotient or fraction of two integers, where the denominator is not zero.
In the case of 4/5, both 4 and 5 are integers. Specifically, 4 is the numerator and 5 is the denominator. Since 5 is not zero, 4/5 fits the definition of a rational number.
Furthermore, rational numbers can also be represented in decimal form, and 4/5 can be calculated to be 0.8. This decimal representation also confirms that 4/5 is a rational number, as 0.8 can be expressed as a fraction (8/10) and further simplified to 4/5.