Average question GRE?

Question

The average daily temperature from 9th to 16th January(both inclusive) was 38.6 C and that from the 10th to 17th January(inclusive) was 39.2 C. what was the temperature on 17th January? I am able to find total temperature as 308.8 C from from 9th to 16th January and 313.6 C from the 10th to 17th January but stuck!

Answer 1

313.6-308.8=4.8 is the difference between 17th and 9th, but you should know the temperature on 9th to calculate temperature on 17th. So more info is needed!

Answer 2

You can find the difference between 17th and 9th, but you can't find the exact degree on the 17th. The answer should be "can't be determined".