Inspired by Paola Ramirez

Algebra Level 4

{ x + y + { z } = 1.1 x + { y } + z = 2.2 { x } + y + z = 3.3 \large{\begin{cases} x+ \lfloor y \rfloor+ \left \{ z \right \}=1.1\\ \lfloor x \rfloor+ \left \{ y \right \}+z=2.2 \\ \left \{ x \right \}+y+\lfloor z \rfloor=3.3 \end{cases}}

Let real numbers x x , y y and z z satisfy the system of equations above. Find the value of 100 x y z 100 xyz .

Notations :


Inspiration .


The answer is 24.

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1 solution

Chew-Seong Cheong
May 10, 2016

{ x + y + { z } = 1.1 x + { x } + y + { z } = 1.1 . . . ( 1 ) x + { y } + z = 2.2 x + { y } + z + { z } = 2.2 . . . ( 2 ) { x } + y + z = 3.3 { x } + y + { y } + z = 3.3 . . . ( 3 ) \begin{cases} x+ \lfloor y \rfloor+ \{ z \}=1.1 & \implies \lfloor x \rfloor + \{ x \} + \lfloor y \rfloor+ \{ z \} = 1.1 & ...(1) \\ \lfloor x \rfloor+ \{ y \}+z=2.2 & \implies \lfloor x \rfloor+ \{ y \}+ \lfloor z \rfloor + \{ z \} = 2.2 & ...(2) \\ \{ x \}+y+\lfloor z \rfloor=3.3 & \implies \{ x \}+ \lfloor y \rfloor + \{ y \}+\lfloor z \rfloor = 3.3 & ...(3) \end{cases}

( 3 ) ( 2 ) ( 1 ) : 2 x 2 { z } = 0 x = { z } The only solution is x = { z } = 0 x = { x } z = z \begin{aligned} (3)-(2)-(1): \quad - 2 \lfloor x \rfloor - 2\{ z \} & = 0 \\ \implies \lfloor x \rfloor & = -\{z\} \quad \quad \small \color{#3D99F6}{\text{The only solution is}} \\ \implies \lfloor x \rfloor & = \{z\} = 0 \\ x & = \{x\} \\ z & = \lfloor z \rfloor \end{aligned}

( 1 ) : { x } + y = 1.1 x = { z } = 0 y = 1 { x } = 0.1 = x ( 2 ) : { y } + z = 2.2 x = { z } = 0 z = 2 = z { y } = 0.2 y = y + { y } = 1.2 \begin{aligned} (1): \quad \{ x \} + \lfloor y \rfloor & = 1.1 \quad \quad \small \color{#3D99F6}{\lfloor x \rfloor = \{z\} = 0 } \\ \implies \lfloor y \rfloor & = 1 \\ \{x\} & = 0.1 = x \\ (2): \quad \{ y \}+ \lfloor z \rfloor & = 2.2 \quad \quad \small \color{#3D99F6}{\lfloor x \rfloor = \{z\} = 0 } \\ \implies \lfloor z \rfloor & = 2 = z \\ \{y\} & = 0.2 \\ \implies y & = \lfloor y \rfloor + \{y\} = 1.2 \end{aligned}

100 x y z = 100 ( 0.1 ) ( 1.2 ) ( 2 ) = 24 \implies 100xyz = 100(0.1)(1.2)(2) = \boxed{24}

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