I only scanned a few problems but I think most of these problems can be solved just by using algebra.

For example, in question one you have three consecutive numbers, so you can call them n, n+1, and n+2. Then, if you put it into context you come up with the equation

2n = (n+2) + 23

Look for key words (for example, "is" usually corresponds to an equals sign) in the equation, and just look at your equation and make sure it makes sense.