Find the missing term 4, 9, 19, __, 79

World War II started that year...

Depends what country you were in.

Anyway, each number is twice the preceding number +1.

The answer is obviously 31.

First, you have to understand that the numbers are hexadecimal.
As such they are all perfect squares.
The sequence becomes 2^2, 3^2, 5^2, ____ , B^2.
2, 3, 5, 7 and B are the first 5 primes.
So the missing number is 7^2 = 31.

If you have any other questions such as how far it is from Winnipeg to Montreal, or who the 31 steps are, i can't help with those I'm afraid.

Don't make it too complicated.

The missing number is 39 as the series is the double of the difference between two successive numbers.

9-4=5
19-9=10
39-19=20
79-39=40