At 2:00 P. M., a thermometer reading 80 degrees F is taken outside, where the are temperature is 20 degrees F. At 2:03 P. M., the temperature reading yielded by the thermometer is 42 degrees F. Later, the thermometer is brought inside, where the are is at 80 degrees F. At 2:10 P. M., the reading is 71 degrees F. When was the thermometer brought indoors?

Question

Brock

Mathematics

29 January, 11:22

At 2:00 P. M., a thermometer reading 80 degrees F is taken outside, where the are temperature is 20 degrees F. At 2:03 P. M., the temperature reading yielded by the thermometer is 42 degrees F. Later, the thermometer is brought inside, where the are is at 80 degrees F. At 2:10 P. M., the reading is 71 degrees F. When was the thermometer brought indoors?

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Rylee Nguyen · Answer 1

We want to know when we brought it back in to the room. at that time the temperature difference is 80 - 42 = 38 so we have to solve

38=9 e ^-.3344t for t

this time we get

38 / 9 = e^ -.3344t

t = ln (38 / 9) / -.3344 t=-4.3

so 4.3 minutes before 2:10