A geologist visits 40 volcanoes in Alaska and California. 15 percent of the volcanoes are in California. How many volcanoes does the geologist visit in California and how many in Alaska?

40 volcanoes = 100% of them

15% were in California so if we want to know how much % were in Alaska we do 100% - 15% which equals 85%, so 85% were in Alaska.

Now to find out how many the geologist visited in each state multiply 40 by the percentage.

Number of volcanoes in California = 15% of 40 volcanoes = 0.15 x 40 = 6
Number of volcanoes in Alaska = 85% of 40 volcanoes 0.85 x 40 = 34

Hope this answers your question, and May The Force Be With You!-Jabba