How to calculate a percentage error between an exact value and an approximate value

Topic 1
Number and Algebra
change topic  Scientific notation and significant figures
 Percentage error
 Using your calculator to solve equations
 Arithmetic sequences
 Arithmetic series and sigma notation
 Geometric sequences
 Geometric series and sigma notation
 Finance (compound interest with formula)
 Finance (compound interest with calculator)
 Finance (amortization and annuities)
 Exponents
 Logarithms and natural logarithms (1 of 2)
 Logarithms and natural logarithms (2 of 2)
 Solving linear and polynomial equations (calculator shortcuts)