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Grade 8 - Mathematics
2.9 Compound Proportion

10 men can lay a road 75 Km. long in 5 days. In how many days can 15 men lay a road 45 Km. long.

Let x be number of days.
Ratio of days = 5:x.
Number of men is inversely proportional to number of days.
So inverse of ratio of men = 15:10 = 3:2.
Length of road is directly proportional to number of days.
Therefore, Ratio of lengths = 75:45 = 5:3
5:x = 3*5:2*3
x*3*5 = 5*2*3
x = (5*2*3)/(3*5)
x = 2.
Number of days required = 2 days.

Directions: Solve the following problems. Also write at least ten examples of your own.
Q 1: The dorm charges $6300, for 35 students for 24 days , in how many days will the dorm charges be $3375 for 25 students.
15 days
17 days
16 days
18 days

Q 2: 175 men can dig a canal 3150m. long in 36 days. How many men are required to dig a canal 3900m. long in 24 days.
330 men
320 men
325 men
315 men

Question 3: This question is available to subscribers only!

Question 4: This question is available to subscribers only!

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