Три пятых плюс одна четвёртых

To add fractions with different denominators, we need to find a common denominator. In this case, the common denominator is the least common multiple (LCM) of 5 and 4, which is 20.

Now we can rewrite the fractions with the common denominator:

Three-fifths (3/5) can be written as 12/20 (by multiplying both numerator and denominator by 4). One-fourth (1/4) can be written as 5/20 (by multiplying both numerator and denominator by 5).

Now, we can add the fractions:

12/20 + 5/20 = (12 + 5)/20 = 17/20.

Therefore, the result of adding three-fifths and one-fourth is seventeen twentieths (17/20).