Identify the given dimensions and calculate the outer radius.

Length (height), $h = 5 \text{ m}$
Inner radius, $r_i = 0.4 \text{ m}$
Outer diameter, $D_o = 1.2 \text{ m}$
Outer radius, $r_o = \frac{D_o}{2} = \frac{1.2 \text{ m}}{2} = 0.6 \text{ m}$
Value of $\pi = 3.14$

The volume of the material in a hollow cylinder is the difference between the outer cylinder's volume and the inner cylinder's volume.
The formula for the volume of a cylinder is $V = \pi r^2 h$.
Volume of material, $V_{\text{material}} = V_o - V_i = \pi r_o^2 h - \pi r_i^2 h = \pi h (r_o^2 - r_i^2)$.

Substitute the values:

We know that $1 \text{ m} = 10 \text{ dm}$.
Therefore, $1 \text{ m}^3 = (10 \text{ dm})^3 = 1000 \text{ dm}^3$.

The correct option is d) $3,140 \text{ dm}^3$.

Question 14: A shopkeeper has a mixture of red sorghum flour and white sorghum flour weighing $40 \text{ kg}$. One type costs $1,900 \text{ FRW}$ per kg and another cost $2,100 \text{ FRW}$ per kg. If the mixture is sold at $2,000 \text{ FRW}$ per kg, find the number of kg of each type.

Let $x$ be the mass (in kg) of the red sorghum flour (costing $1,900 \text{ FRW/kg}$).
Let $y$ be the mass (in kg) of the white sorghum flour (costing $2,100 \text{ FRW/kg}$).

The total mass of the mixture is $40 \text{ kg}$:

The total cost of the mixture, if sold at $2,000 \text{ FRW/kg}$, is $40 \text{ kg} \times 2,000 \text{ FRW/kg} = 80,000 \text{ FRW}$.
The total cost of the ingredients must equal this total cost:

From equation (1), express $y$ in terms of $x$:

Substitute this expression for $y$ into equation (2):

Combine like terms:

Divide by $-200$:

Substitute $x = 20$ into $y = 40 - x$:

So, there are $20 \text{ kg}$ of red sorghum flour and $20 \text{ kg}$ of white sorghum flour.

The correct option is a) $20 \text{ kg}$ and $20 \text{ kg}$.

Question 15: The sum of interior angles of a regular polygon is $1440^\circ$.

a) Find the number of sides of this polygon.

b) Name the polygon.

a) Find the number of sides of this polygon.

The sum of the interior angles ($S$) of a polygon with $n$ sides is given by the formula:

Given $S = 1440^\circ$.

Divide both sides by $180^\circ$:

Add 2 to both sides:

The number of sides of the polygon is $\boxed{\text{10}}$.

b) Name the polygon.

A polygon with 10 sides is called a decagon.