Question

a man spends 2/5 of his salary on food and remaining3/10 on house rent ,electricity etc .what fraction of his salary is still left with him

Answer 1

$let \: salary \: be \: x \\ remaining \: salary = x - \frac{2}{5} x - \frac{3}{10}x \\ = \frac{10x - 4x - 3x}{10} \\ = \frac{10x - 7x}{10} \\ = \frac{3x}{10} \\ hence \: \frac{3}{10} \: salary \: left \: with \: him$