AMC 8 · 2006 · #10

Easy mode Grade 5
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Problem

Jorge's teacher asks him to draw dots on a graph. The dots show all the rectangles with area 1212 whose sides are positive whole numbers.

For each such rectangle, let ww be the width and ll be the length. Jorge plots the point (w,l)(w, l).

So he needs every pair of positive whole numbers (w,l)(w, l) where w×l=12w \times l = 12.

Which of the five graphs shows exactly the right set of dots?

Pick an answer.

(A)
Six points $(1,12), (2,6), (3,4), (4,3), (6,2), (12,1)$ on the curve $wl=12$
(B)
Six points on the diagonal line $l=w$: $(1,1), (3,3), (5,5), (7,7), (9,9), (11,11)$
(C)
Six points on the anti-diagonal line $w+l=12$: $(1,11), (3,9), (5,7), (7,5), (9,3), (11,1)$
(D)
Six horizontal points at height $l=6$: $(1,6), (3,6), (5,6), (7,6), (9,6), (11,6)$
(E)
Six vertical points at $w=6$: $(6,1), (6,3), (6,5), (6,7), (6,9), (6,11)$

AMC 8 2006 problem © Mathematical Association of America (MAA AMC). Reproduced for educational use.

Try it yourself first — the explanation is most useful after you’ve attempted it.