How can you find the answer to a fraction addition problem without using fraction strips?

My answer is preceded by "how do you use fraction strips?" !. The standard way is to adapt the fractions so they all have the same denominator (the "common denominator". So 1/2 + 1/4 is done by changing the 1/2 to 2/4. Total = 2/4 + 1/4 = (2+1)/4 = 3/4. And 2/5 + 1/2 + 1/3 + 1/6 = 12/30 + 15/30 10/30 + 5/30 = 42/30 = 7/5