Table:
2007
2010
2013
2016

percent

middle-aged canadians
81.2
88.0
89.6
96.2

seniors
32.2
46.0
52.4
68.2

percentage points

gap
49.0
41.9
37.2
28.0

Statement: the gap between seniors and middle-aged canadians narrowed substantially by 21 percentage points from 2007 to 2016.
Question: how many percentage points did the gap between seniors and middle-aged canadians narrow from 2007 to 2016?
Answer: [21]