Expert: Wei Chong - 5/13/2008

Question
1penny plus 2 pennies plus 3pennies upto 1 dollar is ???
1penny plus 2 pennies plus 3pennies upto 2 dollars is ???
1penny plus 2 pennies plus 3pennies upto 3 dollars is ???
1penny plus 2 pennies plus 3pennies upto 4 dollars is ???
1penny plus 2 pennies plus 3pennies upto 5 dollars is ???

Answer
Hi Rhonda,

Let's take the first example:
   
1 penny plus 2 pennies plus 3 pennies up to 1 dollar (100 pennies) is ?

We can interpret this question as:

1 + 2 + 3 +....+ 100

Where we are to find the sum of all the pennies.

If you look carefully, the above expression is a sum of a series, the formula to calculate the sum is given as:

  Sum  =  n(n+1)/2 where n = number of terms (n must be even)

So, for the expression above,

Sum  = 100(100+1)/2
    = 50(101)
    = 5050

As for 1penny plus 2 pennies plus 3 pennies up to 2 dollars
(1 + 2 + 3 + ..... + 200)

Sum = 200(200+1)/2
   = 100(201)
   = 20100

You can calculate the sum for the rest...

Best Regards,
Wei Chong
http://www.mathexpression.com/