A child is creating a pyramid with building blocks. The top three levels include 4 blocks, 10 blocks, and 16 blocks.

Part 1: How many blocks would be needed for a pyramid 25 levels tall?
Part 2: Use complete sentences to explain how a sum of an arithmetic series was applied.

Question

A child is creating a pyramid with building blocks. The top three levels include 4 blocks, 10 blocks, and 16 blocks. 

Part 1: How many blocks would be needed for a pyramid 25 levels tall? 
Part 2: Use complete sentences to explain how a sum of an arithmetic series was applied.

anonymous · Answer

anyone~?

raden · Answer

given a1 = 4 and its difference d = 6. then use the formula :
Sn = n/2 (2a1 + (n-1)d)
just put n=25, and the values above into that formula

anonymous · Answer

2400? @RadEn

raden · Answer

Sn = n/2 (2a1 + (n-1)d)
S25 = 25/2 (2*4 + (25-1)6)
S25 = 25/2 * (8 + 144)
S25 = 25/2 *  152
S25 = 1900

anonymous · Answer

ah.. makes more sense.. I appreciate that @RadEn

raden · Answer

okay

anonymous · Answer

any good explanation for part 2 ? @RadEn

anonymous · Answer

I've been doing these for like 5 hours I'm just tired lol