p1. Two integers $m$ and $n$ are said to be [i]coprime [/i] if there are  integers $a$ and $ b$ such that $am + bn = 1$. Show that for each integer $p$, the pair of numbers formed by $21p + 4$ and $14p + 3$ are always coprime.


p2. Two farmers, Person $A$ and Person $B$ intend to change the boundaries of their land so that it becomes like a straight line, not curvy as in image below. They do not want the area of ​​their origin to be reduced. Try define the boundary line they should agree on, and explain why the new boundary does not reduce the area of ​​their respective origins.
[img]https://cdn.artofproblemsolving.com/attachments/4/d/ec771d15716365991487f3705f62e4566d0e41.png[/img]


p3. The system of equations of four variables is given: $\left\{\begin{array}{l}  
23x + 47y - 3z = 434 \\
47x - 23y - 4w = 183 \\
19z + 17w = 91
 \end{array} \right. $
where $x, y, z$, and $w$ are positive integers.
Determine the value of $(13x - 14y)^3 - (15z + 16w)^3$


p4. A person drives a motorized vehicle so that the material used fuel is obtained at the following graph.
[img]https://cdn.artofproblemsolving.com/attachments/6/f/58e9f210fafe18bfb2d9a3f78d90ff50a847b2.png[/img]
Initially the vehicle contains $ 3$ liters of fuel. After two hours, in  the journey of fuel remains $ 1$ liter.
a. If in $ 1$ liter he can cover a distance of $32$ km, what is the distance taken as a whole? Explain why you answered like that?
b. After two hours of travel, is there any acceleration or deceleration? Explain your answer.
c. Determine what the average speed of the vehicle is.


p5. Amir will make a painting of the circles, each circle to be filled with numbers. The circle's painting is arrangement follows the pattern below.
[img]https://cdn.artofproblemsolving.com/attachments/8/2/533bed783440ea8621ef21d88a56cdcb337f30.png[/img]
He made a rule that the bottom four circles would be filled with positive numbers less than $10$ that can be taken from the numbers on the date of his birth, i.e. $26 \,\, - \,\, 12 \,\, - \,\,1961$ without recurrence. Meanwhile, the circles above will be filled with numbers which is the product of the two numbers on the circles in underneath.

a. In how many ways can he place the numbers from left to right, right on the bottom circles in order to get the largest value on the top circle? Explain.

b. On another occasion, he planned to put all the numbers on the date of birth so that the number of the lowest circle now, should be as many as $8$ circles. He no longer cares whether the numbers are repeated or not .

i. In order to get the smallest value in the top circle, how should the numbers be arranged?
ii. How many arrays are worth considering to produce the smallest value?
1. We start with the given system of equations:
   \[
   \begin{cases}
   23x + 47y - 3z = 434 \\
   47x - 23y - 4w = 183 \\
   19z + 17w = 91
   \end{cases}
   \]
   
2. First, solve the third equation for \(z\) and \(w\):
   \[
   19z + 17w = 91
   \]
   We need to find positive integer solutions for \(z\) and \(w\). By inspection or trial and error, we find:
   \[
   z = 3, \quad w = 2
   \]
   Substituting \(z = 3\) and \(w = 2\) into the third equation:
   \[
   19(3) + 17(2) = 57 + 34 = 91
   \]
   This satisfies the equation.

3. Substitute \(z = 3\) into the first two equations:
   \[
   23x + 47y - 3(3) = 434 \implies 23x + 47y - 9 = 434 \implies 23x + 47y = 443
   \]
   \[
   47x - 23y - 4(2) = 183 \implies 47x - 23y - 8 = 183 \implies 47x - 23y = 191
   \]

4. We now have a system of two equations with two variables:
   \[
   \begin{cases}
   23x + 47y = 443 \\
   47x - 23y = 191
   \end{cases}
   \]

5. Solve this system using the method of elimination. Multiply the first equation by 23 and the second equation by 47:
   \[
   23(23x + 47y) = 23(443) \implies 529x + 1081y = 10189
   \]
   \[
   47(47x - 23y) = 47(191) \implies 2209x - 1081y = 8977
   \]

6. Add the two equations to eliminate \(y\):
   \[
   529x + 1081y + 2209x - 1081y = 10189 + 8977 \implies 2738x = 19166 \implies x = \frac{19166}{2738} = 7
   \]

7. Substitute \(x = 7\) back into one of the original equations to find \(y\):
   \[
   23(7) + 47y = 443 \implies 161 + 47y = 443 \implies 47y = 282 \implies y = \frac{282}{47} = 6
   \]

8. We have found the values:
   \[
   x = 7, \quad y = 6, \quad z = 3, \quad w = 2
   \]

9. Calculate the expression \((13x - 14y)^3 - (15z + 16w)^3\):
   \[
   13x - 14y = 13(7) - 14(6) = 91 - 84 = 7
   \]
   \[
   15z + 16w = 15(3) + 16(2) = 45 + 32 = 77
   \]
   \[
   (13x - 14y)^3 - (15z + 16w)^3 = 7^3 - 77^3 = 343 - 456533 = -456190
   \]

The final answer is \(\boxed{-456190}\)