Toothpicks are used to form squares in the pattern shown:

![](https://cdn.mathpix.com/cropped/2024_04_20_6ed09463f225f8ba1f07g-129.jpg?height=138&width=911&top_left_y=256&top_left_x=607)

Four toothpicks are used to form one square, seven to form two squares, and so on. If this pattern continues, how many toothpicks will be used to form 10 squares in a row?
(A) 39
(B) 40
(C) 31
(D) 35
(E) 28

## Part B: Each correct answer is worth 6.
For 1 square, 4 toothpicks are needed.

For 2 squares, 7 toothpicks are needed.

For 3 squares, 10 toothpicks are needed.

So when each additional square (after the first) is added in the pattern, 3 more toothpicks are added. Thus, to form 10 squares, we need to add 9 groups of 3 toothpicks to the original 4 , so we need $4+9(3)=31$ toothpicks in total.

ANSWER: (C)