[tex] \frac{10}{100} \times a = \frac{1}{10} \times a = \frac{a}{10} [/tex]
[tex] \frac{20}{100} \times a = \frac{1}{5} \times a = \frac{a}{5} [/tex]
[tex]m_{a} = 26[/tex]
[tex] \frac{a + \frac{ a }{10} + \frac{a}{5} }{3} = 26 \: | \times 3[/tex]
[tex]a + \frac{a}{10} + \frac{a}{5} = 78 \: | \times 10[/tex]
[tex]10a + a + 2a = 780[/tex]
[tex]13a = 780 \: | \div 13[/tex]
[tex]a = 60[/tex]
