Answer:
3 °C
Step-by-step explanation:
You want the temperature that, when added to four others, changes the mean from 8°C to 7°C.
Mean
The mean is the sum of the values in a data set, divided by the number of values. For the purpose here, we can assume that all of the first four temperatures were their mean. Then the mean after 5 days is ...
(8 +8 +8 +8 +x)/5 = 7
32 +x = 35 . . . . . . . . . . multiply by 5 and simplify
x = 3 . . . . . . . . . . . . subtract 32
The temperature on Jan 5 was 3°C.
