Question 572761
Too bad they didn't have different initials or we could use those for our variable names.  Instead, let's use X and Y.
Jan's current age = X
Jake's current age = Y


Jan is twice as old as Jake:
X = 2Y


The sum of their ages (X + Y) is 5 less than twice Jan's age (2X)
(X + Y) + 5 = 2X


Let's substitute for X in the above equation using X=2Y from before:
((2Y) + Y) + 5 = 2(2Y)  We can remove the parens from the left side since it's all addition:
2Y + Y + 5 = 2(2Y)
combining terms:
3Y + 5 = 4Y
Subtract 3Y from both sides:
5 = Y


Jake is 5.  Since Jan is twice Jake's age, she's 10.


Checking our answer:
The sum of their ages (5 + 10 = 15) is 5 less than twice Jan's age (20). 
15 is 5 less than 20.  
15 = 20 - 5
15 = 15  Correct!