A mountain range has 200 active volcanoes

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?

GSM8K — Grade School Math 8K (Cobbe et al., OpenAI, 2021) · train #2110