Răspuns :
7, 14, 21, 28, 35, 42, 49, 56, 63, 70 - Sunt toate numerele care se impart exact la 7.
70-49=21
63-42=21
56-35=21
49-28=21
42-21=21
35-14=21
28-7=21
70-49=21
63-42=21
56-35=21
49-28=21
42-21=21
35-14=21
28-7=21