Downstream speed = 15 km/h. Upstream speed = 10 km/h. Stream speed = (15-10)/2 = 2.5 km/h.
Total work = 15 × 20 = 300 worker-days. Workers needed = 300/12 = 25.
Let CP = 100. MP = 150. For 25% profit, SP = 125. Discount = (150-125)/150 × 100 = 16.67%.
SI = (20000 × 10 × 2)/100 = 4000. CI = 20000(1.1)² - 20000 = 24200 - 20000 = 4200. Difference = 200.
Combined speed = 50 + 70 = 120 km/h. Time = 360/120 = 3 hours.
Let salary = 100. After increase: 120. After decrease: 120 × 0.9 = 108. Net change = 8%.
This problem involves using the relationship between distance, speed, and time where the same distance is covered in different times at different speeds.
Step 1: Set Up Equations Using Distance Formula
Let the distance be d km and the required time be t hours. Since distance = speed × time, we can write two equations based on the given conditions.
Step 2: Solve for Time
Since both expressions equal d, we set them equal and solve for t.
Step 3: Calculate Distance
Substitute t back into either equation to find d.
The distance to the office is 7.5 km.
Let the distance to the office be d km.
Time taken at 5 km/h:
5
d
hours
Time taken at 6 km/h:
6
d
hours
The difference in arrival times is:
10 minutes late at 5 km/h
5 minutes early at 6 km/h
So, total difference =15 minutes =
60
15
=
4
1
hour.
Thus,
5
d
−
6
d
=
4
1
d(
5
1
−
6
1
)=
4
1
d(
30
6−5
)=
4
1
30
d
=
4
1
d=30×
4
1
=7.5
Therefore, the distance to the office is:
7.5 km
Let CP = 100. MP = 150. SP = 150 × 0.8 = 120. Profit = 20%
Work rate combined = 1/12 + 1/15 = 5/60 + 4/60 = 9/60 = 3/20. Time = 20/3 ≈ 6.67 days
Upstream speed = 30/5 = 6 km/h. Boat speed = Upstream speed + Stream speed = 6 + 2 = 8 km/h