calculations in head

Calculations in the head involve mentally manipulating numbers without external tools. It relies on understanding basic math principles and patterns, such as addition, subtraction, multiplication, and division. People often break complex problems into simpler parts, repeat familiar operations, or use estimation to reach a quick answer. For example, to multiply 20 by 5, you might recognize that 20 is 2 times 10, so 20 x 5 is the same as 2 x 10 x 5, making it easier to compute mentally. These skills improve with practice and help perform arithmetic efficiently without paper or calculators.