A probability problem by atishay jain

Let f ( n ) f(n) be the maximum number of pieces of pizza you can make by n n straight cuts.

Find f ( 1 ) + f ( 2 ) + f ( 3 ) + + f ( 100 ) f(1) + f(2) + f(3) + \cdots + f(100) .


The answer is 171800.

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1 solution

Chew-Seong Cheong
Sep 25, 2017

The maximum number of pieces of pizza from n n cuts is given by (see Cirle Division by Lines ) f ( n ) = 1 2 ( n 2 + n + 2 ) f(n) = \dfrac 12 (n^2+n+2) . Then we have:

S = n = 1 100 1 2 ( n 2 + n + 2 ) = 1 2 n = 1 100 ( n 2 + n + 2 ) = 1 2 ( 100 × 101 × 201 6 + 100 × 101 2 + 2 ( 100 ) ) = 171800 \begin{aligned} S & = \sum_{n=1}^{100} \frac 12(n^2+n+2) \\ & = \frac 12 \sum_{n=1}^{100} (n^2+n+2) \\ & = \frac 12 \left(\frac {100\times101\times 201}6 + \frac {100\times 101}2 + 2(100) \right) \\ & = \boxed{171800} \end{aligned}

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