There are nine unit triangles in the three rows of this triangle. If you add three more rows to the bottom of this triangle so that each row has 2 more unit triangles than the previous row, how many unit triangles will there be?
+73 I hate waiting for moderation... But try counting:
1: 1
2:3
3:5
4:7
5:9
6:11
ALL RIGHT! we have all the rows, just do 7+9+11
16+11
25
25 MORE TRIANGLES
+73 Sorry unit triangles. I meant unit triangles, cuz there are many more bigger triangles than that
+129852 This will be the sum of this series : 1, 3, 5, 7, 9, 11 =
[ First Term + Last Term ] * [ Number of Terms] / 2
[ 1 + 11] * 6 / 2 =
12 * 6 / 2 =
72 / 2 =
36 unit triangles
+37146 You only counted the last three rows.....you didn't include the origianl 3 rows for the total
