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question:Find the number of integers n such that [1 + leftlfloordfrac{120n}{121}rightrfloor = leftlceildfrac{119n}{120}rightrceil.]
answer:Let [ g(n) = leftlceil frac{119n}{120} rightrceil - leftlfloor frac{120n}{121} rightrfloor. ] We investigate changes in g(n) as n increases by 120*121 = 14520 (the least common multiple of the denominators). Note: [ g(n + 14520) = leftlceil frac{119(n + 14520)}{120} rightrceil - leftlfloor frac{120(n + 14520)}{121} rightrfloor ] [ = leftlceil frac{119n}{120} + 119 rightrceil - leftlfloor frac{120n}{121} + 120 rightrfloor ] [ = leftlceil frac{119n}{120} rightrceil + 119 - leftlfloor frac{120n}{121} rightrfloor - 120 ] [ = leftlceil frac{119n}{120} rightrceil - leftlfloor frac{120n}{121} rightrfloor - 1 ] [ = g(n) - 1. ] Thus, each residue class modulo 14520 leads to a decrease in the function value by 1 per period. Therefore, for each residue class r modulo 14520, there is a unique integer n such that g(n) = 1 and n equiv r pmod{14520}. Hence, the total number of integers solving the given equation is boxed{14520}.
question:f the graph of the inverse proportion function y=frac{k}{x} passes through the point left(3,5right), then the graph of the function should be in which quadrant? A: First and third quadrants B: First and second quadrants C: Second and fourth quadrants D: Third and fourth quadr
answer:Given the inverse proportion function y=frac{k}{x}, and it passes through the point left(3,-5right), we aim to determine in which quadrant the graph of this function should be. Step 1: Substitute the given point into the function to find the constant k. [ y=frac{k}{x} Rightarrow -5=frac{k}{3} ] Step 2: Solve for k. [ k = 3 times (-5) = -15 ] Step 3: Analyze the implication of k < 0 for the graph of the function. Since k = -15 < 0, the function y=frac{-15}{x} will produce positive y values when x is negative and negative y values when x is positive. This behavior indicates that the graph of the function will be located in the quadrants where x and y have opposite signs. Step 4: Determine the quadrants. The quadrants where x and y have opposite signs are the second quadrant (where x is negative and y is positive) and the fourth quadrant (where x is positive and y is negative). Therefore, the graph of the function should be in the second and fourth quadrants. Final Answer: boxed{C}.
question:On the lateral sides ( A D ) and ( B C ) of the trapezoid ( A B C D ), points ( P ) and ( Q ) are taken, respectively, with ( A P : P D = 3 : 2 ). The segment ( P Q ) divides the trapezoid into parts, one of which has an area twice that of the other. Find the ratio ( C Q : Q B ) if ( A B : C D = 3 : 2 ).
answer:1. We first extend the non-parallel sides AD and BC of the trapezoid ABCD until they intersect at a point K. 2. By similarity of triangles triangle KDC and triangle KAB, with the similarity ratio given by [ frac{CD}{AB} = frac{2}{3}, ] we find that [ frac{KD}{KA} = frac{2}{3}. ] 3. Let KD = 2x and KA = 3x. Then, [ AD = AK - KD = 3x - 2x = x. ] 4. Given AP: PD = 3: 2, we can determine [ PD = frac{2}{5} AD = frac{2}{5} x. ] 5. Therefore, [ KP = KD + PD = 2x + frac{2}{5}x = frac{10x}{5} + frac{2x}{5} = frac{12x}{5}. ] 6. Assuming the area of the quadrilateral PDCQ is twice the area of APQB, we start with the area relationship [ S_{PDCQ} = 2 S_{APQB}. ] Let S_{triangle KDC} = S. Then, since the trapezoid ABCD shares the area between KDC and KAB, [ frac{S_{triangle KDC}}{S_{triangle KAB}} = left(frac{2}{3}right)^2 = frac{4}{9}, ] leading to [ S_{triangle KAB} = frac{9}{4} S_{triangle KDC} = frac{9}{4} S. ] 7. Considering S_{ABCD} = S_{triangle KAB} - S_{triangle KDC}, [ S_{ABCD} = frac{9}{4} S - S = frac{5}{4} S. ] 8. Given the area proportion, we calculate S_{PDCQ}: [ S_{PDCQ} = frac{2}{3} S_{ABCD} = frac{2}{3} cdot frac{5}{4} S = frac{5}{6} S. ] 9. Similarly for the triangle area: [ S_{triangle KPD} = S + S_{PDCQ} = S + frac{5}{6} S = frac{11}{6} S. ] 10. We take the ratio of areas formed by triangle KDC and triangle KPQ: [ frac{S_{triangle KDC}}{S_{triangle KPQ}} = frac{S}{ frac{11}{6} S } = frac{6}{11}. ] 11. Since also: [ frac{S_{triangle KDC}}{S_{triangle KPQ}} = frac{KD}{KP} cdot frac{KC}{KQ}, ] substituting known values gives: [ frac{2}{frac{12}{5}} cdot frac{KC}{KQ} = frac{5}{6} cdot frac{KC}{KQ} = frac{6}{11}. ] 12. Solving yields: [ frac{KC}{KQ} = frac{36}{55}. ] 13. Thus, since the point lies such that frac{KC}{KB} must be checked, and noting the inequality: [ frac{2}{3} > frac{36}{55}, ] confirming Q lies on the line extending beyond point B. 14. Testing the hypothesis that area A of APQB to be the larger part leads similarly to: [ S_{PDCQ} = frac{1}{3} S_{ABCD} = frac{5}{12} S, ] and verifying areas: [ S_{triangle KPD} = frac{17}{12} S, ] and the ratio: [ frac{S_{triangle KDC}}{S_{triangle KPQ}} = frac{S}{frac{17}{12} S} = frac{12}{17}, ] yielding: [ frac{KC}{KQ} = frac{72}{95}. ] Verifying leads to the correct proportion: # Conclusion: [ boxed{23: 13} ]
question:A person was on trial for a crime on a small island. The court knew that the defendant was born and raised on a neighboring island of knights and liars. (Knights always tell the truth, and liars always lie.) The defendant was allowed to make only one statement in his defense. After considering, he said the following: The person who actually committed the crime I am accused of is a liar. Was this statement reasonable on his part? Did it help his situation or did it worsen it? Perhaps it did not influence the court's decision at all?
answer:1. **Understand the Problem Context**: - The accused on a small island is allowed to make only one statement in defense. - It is known that the accused was born and raised on a neighboring island of knights (who always tell the truth) and liars (who always lie). - The statement made by the accused is: "The person who indeed committed the crime that I am accused of is a liar." 2. **Analyze the Statement for Logical Consistency**: - The goal is to determine if the statement helps the accused or not. 3. **Case 1: Assume the Accused is a Knight**: - **Sub-assumption**: The accused tells the truth (since knights always tell the truth). - **Implication**: - The phrase "The person who indeed committed the crime that I am accused of is a liar" is true. - Therefore, the real criminal must be a liar. - **Conclusion**: - If the real criminal is a liar, and the accused (being a knight) cannot be a liar, then the accused cannot be the real criminal. - Hence, the accused is innocent. 4. **Case 2: Assume the Accused is a Liar**: - **Sub-assumption**: The accused lies (since liars always lie). - **Implication**: - The phrase "The person who indeed committed the crime that I am accused of is a liar" is false (because liars lie). - Therefore, the real criminal cannot be a liar (as the statement must be false), so the real criminal must be a knight. - **Conclusion**: - If the real criminal is a knight, and the accused (being a liar) cannot be one, then the accused cannot be the real criminal. - Hence, the accused is innocent. 5. **General Conclusion**: - In both cases (whether the accused is a knight or a liar), the analysis concludes that the accused cannot be the real criminal based on the truth or falsehood of the statement made. - Therefore, making this statement was reasonable for the accused, as it helped in removing any suspicion from themselves. boxed{text{The statement helped the accused to remove suspicions and assert their innocence.}}