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Problem 805

AMC 10/12, early questions
Geometry Difficulty 3.7 Multiple choice CEMC Pascal · Canada · 2024

In the diagram, ABC\triangle ABC has AB=BC=3x+4AB=BC = 3x+4 and AC=2xAC=2x and rectangle DEFGDEFG has EF=2x2EF = 2x-2 and FG=3x1FG = 3x-1.Figure 0The perimeter of ABC\triangle ABC is equal to the perimeter of rectangle DEFGDEFG. What is the area of ABC\triangle ABC?

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Official solution

Consider the following list of 55 integers, ordered from smallest to largest, and having a median of 1010: a,b,10,c,da,b,10,c,d. Since aa is the smallest integer in the list and dd is the largest, and the list has a range of 77, then dd is 77 more than aa. Since aa and dd differ by 77, then to find the smallest possible value of aa, we can find the smallest possible value of dd and subtract 77. The 55 integers in the list are different from one another, and so the smallest possible value of cc is 11 (cc must be greater than the median 1010), and the smallest possible value of dd is thus 1212. Since dd is 77 more than aa, then the smallest possible integer in the list is 127=512-7=5. (We note that 5,b,10,11,125,b,10,11,12, where bb is greater than 55 and less than 1010, is such a list.)

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Source: CEMC, University of Waterloo, licensed CC-BY-NC-4.0. Statement reproduced verbatim; metadata (topic, difficulty, ordering) added by this project.