Answer:
Allowance = $24
Cost of book = $4.8
Cost of pen = $7.2
Step-by-step explanation:
[tex]Let \ his \ allowance\ be\ x\\\\\frac{1}{5} \ of \ x \ on\ books\\\\\frac{3}{8} \ of \frac{4}{5} \ of \ x\ on \ pen\\\\Balance \ in \ hand = 12[/tex]
[tex]x = \frac{1}{5}x + (\frac{3}{8} \times \frac{4}{5})x +12\\\\x = \frac{1}{5}x + \frac{12}{40} +12\\\\x =\frac{1}{5}x + \frac{3}{10} +12\\\\x - \frac{1}{5}x - \frac{3}{10} =12\\\\\frac{10x - 2x -3x}{10} = 12\\\\\frac{5}{10}x = 12\\\\5x = 12 \times 10\\5x = 120\\x = 24[/tex]
[tex]cost \ of \ book = \frac{1}{5} \times x = \frac{1}{5} \times 24 = 4.8\\\\cost \ of \ pen = \frac{3}{8} \times \frac{4}{5} \times x = \frac{3}{8} \times \frac{4}{5} \times 24 = 7.2[/tex]
