5 goes into 50 10 times, so it was less than 15 years ago. 10 goes into 55 5 and a half times, so it was greater than 10 years ago. At 6, the grandpa was about 8 times older. At 7, the grandpa was about 7 times older. At 8, the grandpa was almost 7 times older. At 9, the grandpa was exactly 6 times as old as the grandson. The grandson was 9 eleven years ago. So, your answer is 11. Hope that helps.
