Jenna is adding black dots to a bunch of white blouses. Each blouse gets 20 dots, and each dot takes 10 ml of black dye. How many 400-ml bottles of dye does Jenna need to buy to dye 100 blouses?
First find the amount of dye each blouse takes: 20 dots/blouse * 10 ml/dot = 
<gadget id="calculator">20*10</gadget>
<output>200</output>
200 ml/blouse.
Then multiply the dye used per blouse by the number of blouses to find the total amount of dye used: 200 ml/blouse * 100 blouses = 
<gadget id="calculator">200*100</gadget>
<output>20_000</output>
20000 ml.
Then divide the amount of dye needed by the amount of dye per bottle to find the number of bottles needed: 20000 ml / 400 ml/bottle = 
<gadget id="calculator">20000/400</gadget>
<output>50</output>
50 bottles.

<result>50</result>