The sum is 37/30 in simplest form, or 1 7/30 as a mixed number.
Decimal: \displaystyle 1.2\overline{3} (the 3 repeats forever, about 1.2333)
Percent: 123.33%
1 whole + 7 of 30 equal parts
Step-by-step solution
The problem
\frac{2}{5} + \frac{5}{6}
Write both fractions over 30. List multiples of each denominator until they meet:
Multiples of 5: 5, 10, 15, 20, 25, 30
Multiples of 6: 6, 12, 18, 24, 30
The least common denominator is 30. Multiply the top and bottom of each fraction by the same number, so its value doesn't change.
Check that it can't be simplified. 37 and 30 have no common factor other than 1, so this is the simplest form.
\text{GCF}(37, 30) = 1
Write it as a mixed number. Divide: 30 goes into 37 1 time with 7 left over. The whole number is 1, the remainder 7 becomes the numerator, and the denominator stays 30.