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Devising a Plan: Solution

Devising a Plan: Solution

Devise a plan to solve the problem.

Solution

We’ve learned how to use Gauss’s method to calculate the sum of the first 100 consecutive numbers. Let’s apply this technique to assist little Jill in determining the number of blocks needed for her wall. In this case, we have only 5050 numbers and the corresponding illustration will look like this:

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Sum of the first and last terms
Sum of the first and last terms

So we have 2525 pairs of numbers that add up to 5151.

The total number of blocks required to make Jill’s triangular wall is:

Number of blocks=25×51=1275\text{Number of blocks} = 25 \times 51 = 1275

Arithmetic series

A sequence of numbers like the one presented in this chapter is called an arithmetic sequence—a sequence of numbers in which the difference between two ...