2009 Grade 8 CEMC Gauss Problems/Problem 22

Problem

A dollar sign is formed by drawing two parallel vertical lines through the letter S, as shown. These lines cut the letter S into $7$ pieces. What is the minimum total number of parallel vertical lines that are needed to cut the letter S into exactly $154$ pieces?


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$\text{ (A) }\ 23 \qquad\text{ (B) }\ 44 \qquad\text{ (C) }\ 22 \qquad\text{ (D) }\ 51 \qquad\text{ (E) }\ 70$

Solution

We can see that the first line cuts the letter S into four pieces ($2$ pieces to the left of the line, and $2$ pieces to the right), and that each additional line adds $3$ more pieces.

This means we can set up a formula in terms of $L$, where $L$ represents the number of lines, and see where the formula is equal to $154$:

$3(L - 1) + 4 = 154$

$3(L - 1) = 150$

$L - 1 = 50$

$L = \boxed {\textbf {(D) } 51}$

~anabel.disher