A mountain range has 200 active volcanoes. In a particular year, 20% of the volcanoes exploded in the first two months, 40% of the remaining exploded by the half of the year, and at the end of the year, another 50% of the volcanoes that hadn't already erupted also exploded. How many mountains are still intact at the end of the year?
By the first two months, 20/100*200 = 
<gadget id="calculator">20/100*200</gadget>
<output>40</output>
40 mountains had erupted.
The total number of mountains remaining after the first round of explosions is 200-40= 
<gadget id="calculator">200-40</gadget>
<output>160</output>
160.
When 40% of the remaining mountains exploded, the number of mountains that were still intact decreased by 40/100*160 = 
<gadget id="calculator">40/100*160</gadget>
<output>64</output>
64.
The number of mountains that hadn't exploded after the second explosions is 160-64 = 
<gadget id="calculator">160-64</gadget>
<output>96</output>
96.
When 50% of the mountains which were still intact exploded, the number of mountains that hadn't erupted was reduced by 50/100*96 = 
<gadget id="calculator">50/100*96</gadget>
<output>48</output>
48.
At the end of the year, 96-48 = 
<gadget id="calculator">96-48</gadget>
<output>48</output>
48 mountains remained intact and hadn't exploded.

<result>48</result>