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# Tip #22 to Get a Top ACT Math Score (page 2)

By McGraw-Hill Professional
Updated on Sep 7, 2011

### Medium

1. By definition the determinant equals ad – bc. What is the value of when m=–2 and n=3 ?
1. –6
2. –13
3. –55
4. –96
5. –102
2. In a recent high school election, the number of votes for three candidates is shown in the following matrix.
3. The school paper reported that the winner received votes in the ratios shown below. Given these matrices, what is the number of juniors who voted for the winner?

1. 0.2
2. 0.3
3. 25
1. 15
2. 10
4. The matrix below shows the lights at a stadium (sections A through H) that are on and off, with 1 representing on and 0 representing off. Based on this information and the information in the matrix, which of the following is true?
1. All lights in sections A to H are on.
2. All lights in sections A to H are off.
3. The lights in sections A, C, and H are off.
4. The lights in sections A, C, and H are on.
5. There are five lampposts at the stadium.

1. A Notice that this question asks for the determinant, which I didn't teach you. That's because the ACT defines it in the question, and you just have to follow the directions that are given. You could get this one even if you never heard of a matrix, as long as you didn't make the connection and freak out. Sometimes ignorance is bliss. On the ACT, always follow the directions that are given in a question; they give you lots of good info. So plug m =–2 and n = 3 into the matrix and follow the directions for the determinant to get (3(–2))(3(3)) – (2(–2))(4(3)) = –54 – (– 48) = – 6
2. K These matrices are just charts showing data. Take a moment to understand the charts, and then the question is easy. In fact, if we dropped the word "matrix" from this question, fewer people would be intimidated, and it'd be ranked easier. So don't ever get intimidated by the word "matrix". It's just a chart of data. Angino won the election with 50 votes. The part of his votes that came from juniors was 0.2, so multiply 50 × 0.2 = 10 votes from juniors.
3. C Again, just a chart of data, like Skill 15. Take a moment to understand the chart and then it's easy. A 1 tells us that the lights in that section are on, and a 0 tells us that they are off. So choice C is correct, the lights in sections A, C, and H are on.
4. H To add matrices, just add the terms that are in the same spot in each matrix. So

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