Definition
Mental calculation
Working out a result mainly by thinking with number facts, patterns, and relationships.
What it means
Mental calculation does not mean guessing or hiding every thought. You choose useful facts and reshape numbers in your mind. A small jotting can help, but the method is driven by number sense rather than a fixed column procedure.
Remember it
Look for number relationships before reaching for a written method.
Example
For 99 + 36, think 100 + 36 − 1. That gives 135 without using a column algorithm.
Watch for
Writing a complete column algorithm is written calculation, even if you can perform each small step mentally.
Common mix-up
Mental calculation can include a quick jotting; it does not require every step to stay invisible.
Exact meaning
Mental calculation finds an exact or estimated result mainly through number relationships and known facts rather than by carrying out a full written standard algorithm or relying on a calculator.