Question

Matt got a dollar on his birthday. On his second birthday he will get the amount from last year's birthday plus as many dollars as he is old. How much would he receive on his birthday when 12 if this pattern is used. I came up with $78 is this right

Answer 1

I will assume you meant, on his first birthday

1st birthday ---- 1
2nd ------------ 1 + 2 = 3
3rd ------------- 3+3 = 6
4th ------------- 6+4 = 10
5th ------------- 10+5 = 15
.....

this is a special sequence called the triangular numers, take a look how billiard balls
would be racked up in the triangle.

sum(n) = n(n+1)/2
so when n=12
sum(12) = 12(13)/2 = 78

You are right
How did you get your answer ?

Answer 2

We did this

1 1
2 3
3 6
4 10
5 15
6 21
7 28
8 36
9 45
10 55
11 66
12 78