Question

A teacher has 100 pencils in a cup. 16 are more sharp than dull. How many are dull and how many are sharp?

Answer 1

X = dull pencils 
y = sharp pencils
x + y = 100
y = x + 16 ~~Plug this back into your original x+y equation.
x+x+16=100 ==> 2x = 84 ==> x = 42. Plug this back into the y = equation
 y = 42 + 16 ==> y = 58.

42 Dull, 58 sharp.