This is one of the problems that we can approach by using the difference and the sum of the numbers. 

It seems Tom has more fish than Jerry. How many more?

Pretend for a second that Jerry gives 2 fish to Tom, then Tom has exactly 5 times as many fish as Jerry. At this point, how many more fish does Tom have? Since Tom has 5 times as many fish as Jerry, he has $5 -1 = 4$ times more fish than Jerry. Try to use this ratio difference (4) to find how many fish Jerry has at this moment. Then use this to find out how many fish each of them have.