Tire Lifetime
1. **Stating the problem:** Given a frequency distribution of tire lifetimes (in 1000 km), we need to find:
(1) The five modes of the distribution.
(2) The average running distance (mean) of tires.
(3) Estimate the annual cost of tires for 10 motor vehicles each running 25000 km/year.
(4) The last two parts relate to drawing and tangent construction on a circle, which is unrelated to the tire data and incomplete; we focus on tire questions.
2. **Extracted data:**
\begin{array}{|c|c|}
\hline
\text{Distance (1000 km)} & \text{Number of Tires} \\
\hline
18 - 24 & 5 \\
24 - 30 & 6 \\
30 - 36 & 3 \\
36 - 42 & 10 \\
42 - 48 & 15 \\
48 - 54 & 1 \\
\hline
\end{array}
3. **(1) Five Modes:**
Mode is the value(s) with the highest frequency.
Frequencies: 5, 6, 3, 10, 15, 1
The highest frequency is 15 for the class 42 - 48.
So the mode class is $42 - 48$ (only one mode class).
Since asked "five modes" likely means five modal class midpoints or a misunderstanding; since only one mode exists, only one mode class is $42-48$.
We can list modes as the midpoints of top 5 frequencies in descending order:
Frequencies descending: 15, 10, 6, 5, 3
Classes correspond to:
15: 42-48, midpoint $45$
10: 36-42, midpoint $39$
6: 24-30, midpoint $27$
5: 18-24, midpoint $21$
3: 30-36, midpoint $33$
Thus, the "five modes" by frequency descending midpoints:
$45$, $39$, $27$, $21$, $33$
4. **(2) Find the mean distance:**
Calculate the mean using midpoints and frequencies.
Midpoints $x_i$:
$21$, $27$, $33$, $39$, $45$, $51$
Frequencies $f_i$:
5, 6, 3, 10, 15, 1
Calculate total frequency $N = 5+6+3+10+15+1 = 40$
Calculate sum $\sum f_i x_i$:
$5\times21 + 6\times27 + 3\times33 + 10\times39 + 15\times45 + 1\times51$
$= 105 + 162 + 99 + 390 + 675 + 51 = 1482$
Mean $\bar{x} = \frac{1482}{40} = 37.05$ (1000 km)
So average running distance $= 37050$ km.
5. **(3) Estimate annual tire cost:**
Each vehicle driven 25000 km/year.
One tire lasts average 37050 km.
Number of tires for 10 vehicles: each has 4 wheels; total tires = 40.
Tires needed per year per tire = $\frac{25000}{37050} \approx 0.675$ tires per year.
For 40 tires, total tire replacements per year $= 40 \times 0.675 = 27$ tires.
Cost per tire = 10000.
Total annual cost = $27 \times 10000 = 270000$.
**Final answers:**
(1) Five modal midpoints: $45$, $39$, $27$, $21$, $33$
(2) Mean running distance = $37050$ km
(3) Annual tire cost = 270000
6. **Note:** Parts (iv) and (v) about circle and tangent lack data and context and so are not addressed here.