Explanation

Total work = Number of labourers x Total days  

Total work = 20 x 8 = 160 units  

Work done in first 4 days = 20 labourers x 4 days  

Work done = 80 units  

Fraction of work completed = Work done / Total work  

= 80 / 160  

= 1 / 2  

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Explanation

Work (in worker-days) = 15 × 12 = 180

Days for 10 workers = 180 ÷ 10 = 18 days.

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Explanation

Total number of students = 45  

Ali's rank from the top = 12th  

To find rank from the bottom we use this formula:  

Rank from bottom = Total students - Rank from top + 1  

Put the values:  

Rank from bottom = 45 - 12 + 1  

Rank from bottom = 33 + 1  

Rank from bottom = 34  

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Explanation

Let sister’s age = x, Sara’s age = 2x

x + 2x = 36 → 3x = 36 → x = 12 → Sara’s age = 24 years.

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Explanation

Father is 36 years older than son. 

So father's present age = x + 36 years

After 6 years:

Son's age = x + 6 years

Father's age = x + 36 + 6 = x + 42 years

Given: In 6 years, father's age will be 3 times the age of his son.

So, x + 42 = 3 * (x + 6)

Solve the equation:

x + 42 = 3x + 18

42 - 18 = 3x - x

24 = 2x

x = 12

Son's present age = 12 years

Father's present age = x + 36 = 12 + 36 = 48 years

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