If 15 men take 12 days to build a certain type of house, how long would 18 men take to build the same type of house? 2. At a speed of 18 km/h, Shafa takes 30 minutes to ride his bike to school. How long would he take at a speed of:

Given that 15 men take 12 days to build a house:

$$\text{Total work} = \text{Number of men} \times \text{Number of days}$$ $$\text{Total work} = 15 \text{ men} \times 12 \text{ days} = 180 \text{ man-days}$$

To find out how long 8 men would take, divide the total work by the new number of men:

$$\text{Time} = \frac{\text{Total work}}{\text{Number of men}} = \frac{180 \text{ man-days}}{8 \text{ men}} = 22.5 \text{ days}$$

It would take 22.5 days for 8 men to build the same type of house.

2. Shafa's Bike Ride

First, we need to find the distance to Shafa's school using the initial speed and time. Then, we can calculate the time taken for different speeds.

Shafa's initial speed is 18 km/h and the time taken is 30 minutes. Convert 30 minutes to hours:

$$30 \text{ minutes} = \frac{30}{60} \text{ hours} = 0.5 \text{ hours}$$

Now, calculate the distance using the formula $\text{Distance} = \text{Speed} \times \text{Time}$:

$$\text{Distance} = 18 \text{ km/h} \times 0.5 \text{ hours} = 9 \text{ km}$$

The distance to Shafa's school is 9 km.

Now, calculate the time taken at different speeds:

a) At a speed of 9 km/h:

$$\text{Time} = \frac{\text{Distance}}{\text{Speed}} = \frac{9 \text{ km}}{9 \text{ km/h}} = 1 \text{ hour}$$

This is equivalent to $1 \times 60 = 60$ minutes.
It would take 1 hour (or 60 minutes) at 9 km/h.

b) At a speed of 20 km/h:

$$\text{Time} = \frac{\text{Distance}}{\text{Speed}} = \frac{9 \text{ km}}{20 \text{ km/h}} = 0.45 \text{ hours}$$

To convert to minutes: $0.45 \text{ hours} \times 60 \text{ minutes/hour} = 27 \text{ minutes}$.
It would take 0.45 hours (or 27 minutes) at 20 km/h.

c) At a speed of 14 km/h:

$$\text{Time} = \frac{\text{Distance}}{\text{Speed}} = \frac{9 \text{ km}}{14 \text{ km/h}} \approx 0.6428 \text{ hours}$$

To convert to minutes: $0.6428 \text{ hours} \times 60 \text{ minutes/hour} \approx 38.57 \text{ minutes}$.
It would take approximately 0.64 hours (or 38.57 minutes) at 14 km/h.