Shailen is adding three numbers he gets a sum that is an even number between 10 and 20 show two addition equation shailen could have written

Let these there numbers be assigned to variables x, y and z. Since you want to find the sum, add all numbers. However, the sum has boundaries between 10 and 20. Therefore, you will have to use inequality symbols. The two addition equations that could be formulated are:

x+y+z > 10
x+y+z < 20