Question

If a person puts 1 cent in a piggy bank on the first day, 2 cents on the second day, 3 cents on the third day, and so forth, how much money will be in the bank after 40 days? $8.20 $16.40 $0.40 $4.10

Answer 1

this is an arithmetic sequence with the common difference being 1

and if u have 1 cent on day 1 and 2 cents on day 2....then on day 40, u would have 40 cents....but we need the sum of all the days..

the sum of an arithmetic sequence can be found using the formula :
sn = n(a1 + an) / 2
n = number of terms = 40
a1 = first term = 1
an = last term = 40

now we sub
s(40) = 40(1 + 40) / 2
s(40) = 40(41)/2
s(40) = 1640/2
s(40) = 820.....820 cents = $ 8.20 <== the sum