Each level of a smartphone app adds more gems for you to match. On level one, there were 13 gems. On level twelve, there were 123 gems. When you complete all twelve levels, how many total gems will you have matched? A. 605 B. 660 C. 748 D. 816

Level : 1,2,3,4,5,6,7,8,9,10,11,12

Gems : 13 to 123

We have to increase from 13 to 123 over a span of 11 levels.

That's an increase of 110 over 11 levels.

110 / 11 = 10

So we go up 10 gems each level Level : 1,2,3,4,5,6,7,8,9,10,11,12

Gems : 13 23 33 43 53 63 73 83 93 103 113 123