On January 22 in 1943, the town of Spearfish, South Dakota, set the record for the world’s fastest temperature change.



At 7:30 a.m., the temperature was `-4`°F.

By 7:32 a.m., the temperature was `45`°F.

By 9:00 a.m. the same day, the temperature was `54`°F.

By 9:27 a.m., the temperature was `-4`°F.



How many degrees did the temperature change each minute from 7:30 to 7:32?