Question

To predict volcanic eruptions scientists may use a seismograph to detect small earthquakes out of the 169 active volcanoes in the U.S. about 130 are in Alaska. About how many active U.S. volcanoes are not is Alaska?

Answer 1

39 (169-130) - a simple subtraction

Answer 2

39 active volcanoes.

Explanation:

Subtract 169 (whole) from 130 (part). 9 - 0 = 9, 6 - 3 = 3, and 1 - 1 = 0. Therefore, 169 - 130 = 39