A girl spent two fifth of her monthly income for family expense, one third for charity and remaining for saving. What fraction of her income does she save?
1 - 2 / 5 - 1 / 3 =
1 - 3 * 2 / 3 * 5 - 5 * 1 / 5 * 3 =
1 - 6 / 15 - 5 / 15 =
1 - 11 / 15 =
15 / 15 - 11 / 15 = 4 / 15