## Task 4 - 320624

A rectangular children's room is $4 \mathrm{~m}$ and $40 \mathrm{~cm}$ long and $3 \mathrm{~m}$ and $30 \mathrm{~cm}$ wide. It has exactly one door, which is $90 \mathrm{~cm}$ wide. Thomas wants to install a new baseboard around the walls of this room. He calculates the required total length of the wood for the baseboard by considering the given measurements.

The running meter of baseboard wood costs 5 DM. Thomas buys the total length he calculated and pays with a hundred-mark note.

How much money does he get back?
Thomas calculates, taking into account the length $\mathrm{a}=4.40 \mathrm{~m}$, the width $\mathrm{b}=3.30 \mathrm{~m}$ of the room, and the door width $\mathrm{t}=0.90 \mathrm{~m}$, the required total length $2 a+2 b-t=8.80 \mathrm{~m}+6.60 \mathrm{~m}-0.90 \mathrm{~m}=$ $14.50 \mathrm{~m}$.

For this, $5 \cdot 14.50 \mathrm{DM}=72.50 \mathrm{DM}$ need to be paid. Therefore, Thomas receives $100 \mathrm{DM}-72.50 \mathrm{DM}=27.50 \mathrm{DM}$ back.

Solutions of the II. Round 1993 adopted from [5]

### 3.34 XXXIII. Olympiad 1993

### 3.34.1 I. Round 1993, Class 6