+8581 Carmen is playing with blocks. She arranges stacks of blocks so that each successive level of blocks has 1 fewer block than the level below it and the top level has 1 block. Such a stack with 3 levels is shown below. Carmen wants to make sure a stack with 12 levels. How many blocks would she use to build this stack?
Okay, So.. The answer is 78. But, could someone please show me as to why?
Thank you (:
+4082 I have no idea... The only thing that I thought is that she must've made a hole in the floor...
+33616 Start at the top and work down:
level 1: 1 block
level 2: 2 blocks so 1 + 2 = 3 blocks in total
level 3: 3 blocks so 1 + 2 + 3 = 6 blocks in total
...
level n: n blocks so 1+2+3...+n blocks in total.
Now 1+2+3+...+n = n(n+1)/2 so when n = 12 n(n+1)/2 = ?
.
