Math CentralQuandaries & Queries


Question from a student:

A man spends 80% of his income. His income increases by 40% and his expenditure also increases by 25%. Find the percentage increase in his savings?


Suppose that man's income is $x$ units. He spends 80% of his income and saves 20%, thus he spends $0.8 \times x$ units and saves $0.2 \times x$ units. His income increases by 40% and thus his new income is

\[ X = 0.4 \times x = 1.4 \times x \mbox{ units.}\]

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