Terry is drawing isosceles triangles with side lengths a, b, and c such that a = y − x
b = x + z
c = y − z

Where x, y, and z are positive integers and x + y + z < 10.
Find all the possible triples (a, b, c) that satisfy this. 

The distribution of the amount of money spent by students for textbooks in a semester is approximately normal in shape with a mean of $235 and a standard deviation of $20. according to the standard deviation rule, how much did almost all (99.7%) of the students spend on textbooks in a semester?