[tex]\text {Fraction of his money left = } 1 - \dfrac{1}{4} - \dfrac{1}{5} [/tex]
[tex]\text {Fraction of his money left = } \dfrac{20}{20} - \dfrac{1 \times 5}{4 \times 5} - \dfrac{1 \times 4}{5 \times 4} [/tex]
[tex]\text {Fraction of his money left = } \dfrac{20}{20} - \dfrac{5}{20} - \dfrac{4}{20} [/tex]
[tex]\text {Fraction of his money left = } \dfrac{20 - 5 - 4}{20} [/tex]
[tex]\text {Fraction of his money left = } \dfrac{11}{20} [/tex]
