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?

Guest Jun 22, 2019

#1**-3 **

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

CuteDramione Jun 22, 2019

#2**-3 **

Sorry unit triangles. I meant unit triangles, cuz there are many more bigger triangles than that

CuteDramione
Jun 22, 2019

#3**+1 **

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

CPhill Jun 22, 2019

#5

#8**+1 **

You only counted the last three rows.....you didn't include the origianl 3 rows for the total

ElectricPavlov
Jun 22, 2019