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1) If 12 men can cut a lawn in 3 days, in how many days can 4 men cut the same lawn if they work at the same rate?

2) The ratio of cement to sand in a mortar is 5:2. If the cement is 25 kg, what is the weight of the sand?

3) If 12 men can dig a trench in 8 days, how many men can dig it in 6 days at the same rate?

4) If 6 men do a piece of work in 3 days, how many men will be needed to do it in 2 days?

5) A student reads an average of 5 pages of a book per day. How many pages did he read in 3 weeks?

6) A plot of ground can be ploughed by 7 ploughs in 21 days. How long will 5 of the same machines take to plough twice as much ground?

7) A bridge is to be constructed by 120 men in 180 days. If the bridge is to be completed in 150 days, how many more men are required?

8) If 330 men are required to construct 30 km of railway track in 9 months, how long will it take 275 men, working at the same rate, to construct 150 km of track?

9) A boy is 5 times as old as a girl. If their total age is 48 years, how old is the girl?

Answer :

Sure! Let's break down each problem and explain how we can find the answers step-by-step:

1) If 12 men can cut a lawn in 3 days, in how many days can 4 men cut the same lawn if they work at the same rate?

- First, we calculate the total amount of work required, which is equivalent to the number of men (12) multiplied by the number of days (3) they work, resulting in [tex]\(12 \times 3 = 36\)[/tex] man-days.
- To find out how many days it will take 4 men to complete the same work, we divide the total man-days by the number of men: [tex]\(\frac{36}{4} = 9\)[/tex] days.

2) The ratio of cement and sand in a mortar is 5:2. If the cement is 25kg, what is the weight of the sand?

- The total ratio of cement to sand is [tex]\(5 + 2 = 7\)[/tex] parts.
- If the cement represents 5 parts, we can find 1 part by dividing the cement weight by its number of parts: [tex]\(\frac{25 \, \text{kg}}{5} = 5 \, \text{kg per part}\)[/tex].
- Since sand is 2 parts, the sand's weight is [tex]\(2 \times 5 \, \text{kg} = 10 \, \text{kg}\)[/tex].

3) If 12 men can dig a trench in 8 days, how many men can dig it in 6 days at the same rate?

- The total work is [tex]\(12 \times 8 = 96\)[/tex] man-days.
- To find out how many men are required to complete the job in 6 days, we divide the total man-days by the number of days: [tex]\(\frac{96}{6} = 16\)[/tex] men.

4) If 6 men do a piece of work in 3 days, how many men will be needed to do it in 2 days?

- The total work is [tex]\(6 \times 3 = 18\)[/tex] man-days.
- To find the number of men needed to complete the work in 2 days, we use: [tex]\(\frac{18}{2} = 9\)[/tex] men.

5) A student reads an average of 5 pages of a book per day. How many pages did he read in 3 weeks?

- There are 7 days in a week, so in 3 weeks, there are [tex]\(3 \times 7 = 21\)[/tex] days.
- The total pages read are [tex]\(5 \times 21 = 105\)[/tex] pages.

6) A plot of ground can be ploughed by 7 ploughs in 21 days. How long will 5 of the same machines take to plough twice as much ground?

- Ploughing twice as much ground would require double the work, which is [tex]\(7 \times 21 \times 2 = 294\)[/tex] plough-days.
- With 5 ploughs, the time taken is [tex]\(\frac{294}{5} = 58.8\)[/tex] days.

7) A bridge is to be constructed by 120 men in 180 days. If the bridge is to be completed in 150 days, how many more men are required?

- The total work is [tex]\(120 \times 180 = 21600\)[/tex] man-days.
- To complete the work in 150 days, the number of men needed is [tex]\(\frac{21600}{150} = 144\)[/tex].
- The additional men required: [tex]\(144 - 120 = 24\)[/tex] men.

8) If 330 men are required to construct a 30 km track of railway in 9 months, how long will it take 275 men, working at the same rate, to construct 150 km of track?

- The total work for 30 km is [tex]\(330 \times 9 = 2970\)[/tex] man-months.
- To find out how long it takes 275 men to construct 150 km, we establish work proportionality: set up the ratios, solve to find [tex]\(\frac{150 \times 275}{2970} \approx 13.89\)[/tex] months.

9) A boy is 5 times as old as a girl. If their total age is 48 years, how old is the girl?

- Let the girl's age be [tex]\(x\)[/tex]. Then the boy's age is [tex]\(5x\)[/tex].
- The equation is [tex]\(x + 5x = 48\)[/tex], which simplifies to [tex]\(6x = 48\)[/tex].
- Solving for [tex]\(x\)[/tex], the girl's age is [tex]\(x = \frac{48}{6} = 8\)[/tex] years.

I hope this explanation is clear and helps you understand each solution!

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