In the engineering department, 70% of the students are men and 180 are women. How many men are there?
The percentage for women is 100% - 70% = 30%.
Since 180 represents 30%, then 180/30 = 6 students represent 1%.
Hence, 6 x 70 = 
<gadget id="calculator">6*70</gadget>
<output>420</output>
420 students are men.

<result>420</result>