Aunt Zhang bought 4.5 kilograms of apples, paid 50 yuan, and got back 27.5 yuan. How much is an apple per kilogram?
张大妈买了4.5千克苹果，付出50元，找回27.5元．每千克苹果多少元？
<gadget id="calculator">50 - 27.5</gadget>
<output>22.5</output>

<gadget id="calculator">22.5 / 4.5</gadget>
<output>5</output>

<result>5</result>