Question 17: Two buses start from the same station at 9:00 a.m. and travel in opposite directions. The first bus travels at 72 km/h and the second at 48 km/h. We need to find the time when they will be 240 km apart. Question 18: A cuboid has length 7 cm, width 5 cm, and height 4 cm. We need to calculate its total surface area.

1. Problem Description

Question 17: Two buses start from the same station at 9:00 a.m. and travel in opposite directions. The first bus travels at 72 km/h and the second at 48 km/h. We need to find the time when they will be 240 km apart.

Question 18: A cuboid has length 7 cm, width 5 cm, and height 4 cm. We need to calculate its total surface area.

2. Solution Steps

Question 17:

The buses are traveling in opposite directions, so their speeds add up to find their relative speed.

Relative speed = $72 \text{ km/h} + 48 \text{ km/h} = 120 \text{ km/h}$.

Let $t$ be the time in hours it takes for them to be 240 km apart.

Distance = Speed $\times$ Time, so $240 = 120t$.

$t = \frac{240}{120} = 2$ hours.

The buses started at 9:00 a.m., so they will be 240 km apart at 9:00 a.m. + 2 hours = 11:00 a.m.

Question 18:

The formula for the total surface area of a cuboid is:

$2(lw + lh + wh)$, where $l$ is the length, $w$ is the width, and $h$ is the height.

$l = 7 \text{ cm}$, $w = 5 \text{ cm}$, and $h = 4 \text{ cm}$.

Surface area = $2(7 \times 5 + 7 \times 4 + 5 \times 4)$

Surface area = $2(35 + 28 + 20)$

Surface area = $2(83)$

Surface area = $166 \text{ cm}^2$

3. Final Answer

Question 17: C. 11:00 am

Question 18: B. 166 cm²