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9 Cards in this Set
- Front
- Back
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What's the units digit for 374 ^ 3 |
4, take 4 ^ 3 to get units |
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What's the unit digit of 5879 * 1642? |
2 * 9 = 18. So 8. |
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What's the unit digit of 345 + 262 + 149? |
5 + 2 + 9 = 16. So 6. |
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How do you find the units digit of a positive integer to a power? e.g. 8^x or 3^x |
They all have a repeating units pattern. Max of 4 so just need to calc first 4 units for any number. |
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How should you approach sequence problem such as: Xn = 2X(n-1) - 1. If X(1) = 3 what is X(20) - X (19)? |
Find first few terms of the sequence. Find a patter between differences to solve for X(20) - X (19). The difference is always 2^(n-1) in this case so 2 ^ 19 |
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How should you approach sequence problem such as: An = 1 / (n(n+1)) what is the sum of the first 100 elements. |
Start calculating the sequence along with the sum (or whatever is asked) along with the sequence to find the pattern. In this case the summing patter in the sum for the first n terms is n/(n+1). So 100/101. |
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How should you approach sequence problem such as: What is the remainder when 5 ^ x is divided by y? 1. x = 3 2. y = 4 |
Calculate if there's a pattern. Should spot 5 ^ x always has a units digit of 5 (5, 25, 125, 625). This means if you know y the remainder will always be consistent. In this case the remainder when divided by 4 is always 1. So the answer is B. |
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What is the unit digit for any of these numbers raised to a power? 1, 5, 6, 0, 10 |
It's the digit itself. So 5 is always units of 5. 6 is always units of 6. |
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When you're plugging in for problem solving what strategy should you use? When should you make an exception to this rule? |
Always Start with Answer Choice C. This will guide you whether to go up or down. Exception should be made if all the numbers are gross and one is around number which is easier to work with. |
