Question

You finally get an allowance . You put $2 away in January, 4$ away in February, $8 away in March, $16 away in April and followed this saving pattern through to December. How much money do you have in 12 months? Please explain

Answer 1

Google "geometric series" or "sum of geometric series"
here r = 2
and your first value a = 2
and you do it 12 times

Answer 2

For example
http://www.purplemath.com/modules/series5.htm

Answer 3

360