p1. Find all real numbers $x$ that satisfy the inequality $$\frac{x^2-3}{x^2-1}+ \frac{x^2 + 5}{x^2 + 3} \ge \frac{x^2-5}{x^2-3}+\frac{x^2 + 3}{x^2 + 1}$$ p2. It is known that $m$ is a four-digit natural number with the same units and thousands digits. If $m$ is a square of an integer, find all possible numbers $m$. p3. In the following figure, $\vartriangle ABP$ is an isosceles triangle, with $AB = BP$ and point $C$ on $BP$. Calculate the volume of the object obtained by rotating $ \vartriangle ABC$ around the line $AP$ p4. A class farewell event is attended by $10$ male students and $ 12$ female students. Homeroom teacher from the class provides six prizes to randomly selected students. Gifts that provided are one school bag, two novels, and three calculators. If the total students The number of male students who received prizes was equal to the total number of female students who received prizes. How many possible arrangements are there of the student who gets the prize? p5. It is known that $S =\{1945, 1946, 1947, ..., 2016, 2017\}$. If $A = \{a, b, c, d, e\}$ a subset of $S$ where $a + b + c + d + e$ is divisible by $5$, find the number of possible $A$'s.
Problem
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Tags: algebra, geometry, combinatorics, number theory, indonesia juniors
07.11.2021 17:54
parmenides51 wrote: p5. It is known that $S =\{1945, 1946, 1947, ..., 2016, 2017\}$. If $A = \{a, b, c, d, e\}$ a subset of $S$ where $a + b + c + d + e$ is divisible by $5$, find the number of possible $A$'s.
07.11.2021 18:39
parmenides51 wrote: p2. It is known that $m$ is a four-digit natural number with the same units and thousands digits. If $m$ is a square of an integer, find all possible numbers $m$.
07.11.2021 23:55
parmenides51 wrote: p4. A class farewell event is attended by $10$ male students and $ 12$ female students. Homeroom teacher from the class provides six prizes to randomly selected students. Gifts that provided are one school bag, two novels, and three calculators. If the total students The number of male students who received prizes was equal to the total number of female students who received prizes. How many possible arrangements are there of the student who gets the prize?
08.11.2021 01:38
Hint
08.11.2021 03:25
$$\frac{x^2-3}{x^2-1} + \frac{x^2 + 5}{x^2 + 3} \ge \frac{x^2-5}{x^2-3} + \frac{x^2 + 3}{x^2 + 1} $$$$\implies \left(\frac{x^2 + 5}{x^2 + 3} - \frac{x^2-5}{x^2-3}\right) + \left(\frac{x^2-3}{x^2-1} - \frac{x^2 + 3}{x^2 + 1}\right) \ge 0 $$$$ \implies 4x^2 \left(\frac{1}{x^4-9} - \frac{1}{x^4-1}\right) \ge 0 $$$$\implies \frac{32x^2}{(x^4-9) \cdot (x^4-1)} \ge 0$$$$\implies (x^4-9) \cdot (x^4-1) > 0 $$$$\implies x^4-9 > 0 \text { or } x^4-1 < 0 $$ The solution set shall be $$(- \infty, -\sqrt{3}) \cup (-1, 1) \cup (\sqrt{3}, +\infty)$$.
08.11.2021 05:40
P3
13.07.2022 03:33
in p4, there are other possible cases. 2 boys 2 girls and 1 boy 1 girl