Question

If Php10 is saved on October 1, Php20 on October 2, Php30 on October 3, and so on, how much is saved during October?

Answer 1

4960

Explanation:

let `Php(day)=10*day iff Php_((1))=10 , Php_((2))=20 , ...`
As you may noticed, this is an arithmetic progression, where:
`a_1=10`
`d=10`
`n=31` (31 days on October)

So we want the Sum of this progression, which is given by the function `Sum=(n/2)*(2a_1+(n-1)d)`

Thus:
`Sum=(31/2)*(2*10+(31-1)*10)=31/2*(20+300)=31/2*320=31*160=160*30+160=4800+160=4960`