Question

A child is creating a pyramid with building blocks. The top three levels include 5 blocks, 12 blocks, and 19 blocks.

Part 1: How many blocks would be needed for a pyramid 25 levels tall? (5 points)

Part 2: Use complete sentences to explain how a sum of an arithmetic series was applied. (4 points)

Answer 1

level 1: 5 blocks
level 2: 12 = 5+7*1
level 3: 19=5+7*2
.....
level n: how many blocks u think are there?

Answer 2

level 3: 26
level 4: 33
level 5: 40
level 6: 47
level 7: 54
level 8: 38
? that correct going up?

Answer 3

yes and the general eqn for n level is 5+7*(n-1) ok?

Answer 4

yes and that would be for part 2 thank you

Answer 5

welcome - what about part 1? :)

Answer 6

i would just keep on going up

Answer 7

thats one way of doing it....but theres an easier way....

Answer 8

notice every level, there are 5+something blocks...so for 25 levels, it would be 25*(5)+something block right?

Answer 9

ok 180 blocks

Answer 10

try again pl? 25*5 is....

Answer 11

125

Answer 12

:) good...so now we have to add the +something part of each level...okay?

Answer 13

+7?

Answer 14

well +7 is part of it but it is +7*(n-1) for n level right?

Answer 15

so +7*(25-1)?

Answer 16

That is correct for the 25th level :) so all we need is to add from 1,2,3...to 25 levels to find the total...ok?

Answer 17

Nope...do u understand everything up to this point first? :)

Answer 18

yea

Answer 19

OK so adding them together...7*0+7*1+7*2+.....7*(25-1), we can group them and it becomes 7*(0+1+2+....+24) okay?

Answer 20

25*5+(12*24+12)*7 do this and i get the answer?

Answer 21

hahahaha u already know the eqn for an arithmetic series? u hardly need my help :P

Answer 22

n yes, ur ans is right - good job!

Answer 23

2225 thats it

Answer 24

u got it :)

Answer 25

thanks

Answer 26

i hate writing complete sentences....u good for part 2 i hope? ;)

Answer 27

kind of

Answer 28

cool - let me look at ur new Q....not sure i have enough time...