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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?

 

 Jun 22, 2019
 #1
avatar+75 
-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

 Jun 22, 2019
 #2
avatar+75 
-3

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

CuteDramione  Jun 22, 2019
 #3
avatar+106535 
+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

 

 

cool cool cool

 Jun 22, 2019
 #4
avatar+75 
-3

what did i do wrong... :(

CuteDramione  Jun 22, 2019
 #5
avatar+19914 
0

1+3+5+7+9+11 = 36 total unit triangles 

 Jun 22, 2019
 #6
avatar+75 
-2

I did something wrong?

CuteDramione  Jun 22, 2019
 #8
avatar+19914 
0

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

ElectricPavlov  Jun 22, 2019
 #7
avatar+75 
-2

OHHHH IN TOTAL! I THOUGHT HOW MANY MORE

 Jun 22, 2019

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