How can you find the sum of 2z-20 and 3z plus 5?

Answer 1

Add like terms to like:

(2z - 20) + (3z + 5) = (2z + 3z) + (-20 + 5)

= 5z - 15

2z is shorthand for z+z, 3z is shorthand for z+z+z, so:

2z + 3z = (z+z) + (z+z+z)

= z+z+z+z+z

= 5z

Or, to put it another way, just add the coefficients:

2z + 3z = (2+3)z

= 5z.