From 1-100, take two different numbers so that their sum is a multiple of 9. How many different ways are there?
从1-100中，取两个不同的数，使其和是9的倍数，有多少种不同的取法？
<gadget id="calculator">100 / 2</gadget>
<output>50</output>

<gadget id="calculator">11 * 50</gadget>
<output>550</output>

<result>550</result>