Mental Math

Students can sometimes procedurally solve arithmetic problems but have to use different skills when asked to compute 85 x 99 without a pencil.
The idea of 99 x 85 being equivalent to 100 x 85 - 1 x 85 is a different non-mechanical way of thinking for many students. The mechanics of Mathematics are important -- however, when used in conjunction with mental Math and clever but easier procedures, students are empowered and become more confident and self-reliant.