Percentage
- If 24-carat gold is considered to be hundred per cent pure gold, then the percentage of pure gold in 22-carat gold is :
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∵ 24 = 100%
∴ 22 = 100 × 22 = 91 2 % 24 3 Correct Option: B
∵ 24 = 100%
∴ 22 = 100 × 22 = 91 2 % 24 3
- In a class, the average score of girls in an examination is 73 and that of boys is 71. The average score for the whole class is 71.8. Find the percentage of girls.
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Let the number of boys be x and that of girls be y.
Then, 71x + 73y = 71.8 (x + y)
⇒ 71.8x – 71x = 73y – 71.8y
⇒ 0.8x = 1.2y⇒ x = 1.2 = 12 = 3 y 0.8 8 2 ⇒ x + 1 = 3 + 1 ⇒ x + y = 5 y 2 y 2
∴ Percentage of girls= y × 100 = 2 × 100 = 40% x + y 5 Correct Option: A
Let the number of boys be x and that of girls be y.
Then, 71x + 73y = 71.8 (x + y)
⇒ 71.8x – 71x = 73y – 71.8y
⇒ 0.8x = 1.2y⇒ x = 1.2 = 12 = 3 y 0.8 8 2 ⇒ x + 1 = 3 + 1 ⇒ x + y = 5 y 2 y 2
∴ Percentage of girls= y × 100 = 2 × 100 = 40% x + y 5
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Shelf A has 4 of the number of 5
books that shelf B has. If 25% of the books in A are transferred to B and then 25% of the books from B are transferred to A, then the percentage of the total number of books that A will have is
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Let the number of books in shelf B be 100.
∴ Number of books in shelf A = 80
On transferring 25% i.e.1 of books of shelf A to shelf B. 4
B = 100 + 20 = 120
Again, on transferring1 of books of shelf B to shelf A. 4 A = 60 + 120 = 90 4
∴ Required percentage= 90 × 100 = 50% 180 Correct Option: B
Let the number of books in shelf B be 100.
∴ Number of books in shelf A = 80
On transferring 25% i.e.1 of books of shelf A to shelf B. 4
B = 100 + 20 = 120
Again, on transferring1 of books of shelf B to shelf A. 4 A = 60 + 120 = 90 4
∴ Required percentage= 90 × 100 = 50% 180
- The tax on an article decreases by 10% and its consumption increases by 10%. Find the effect per cent on its revenue.
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Let the original consumption be 1 unit & tax on it be ₹100.
So, revenue = ₹(100 × 1) = ₹100.
New consumption= 
110 × 1 
= 11 units. 100 10
Now, tax on 1 unit = ₹90Tax on 11 units 10 = 90 × 11 = ₹ 99. 10
∴ Decrease in revenue = 1 %Correct Option: C
Let the original consumption be 1 unit & tax on it be ₹100.
So, revenue = ₹(100 × 1) = ₹100.
New consumption= 110 × 1 = 11 units. 100 10
Now, tax on 1 unit = ₹90Tax on 11 units 10 = 90 × 11 = ₹ 99. 10
∴ Decrease in revenue = 1 %
- Find the total output of a coalmine, if after 24% wastage the net output is 68,400 tonnes.
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Let the total output be x tonnes.
Then, net output= x - 24 × x = 76x 100 100 ⇒ 76 = 68,400 100 ⇒ x = 68,400 × 100 = 90,000 tonnes. 76 Correct Option: C
Let the total output be x tonnes.
Then, net output= x - 24 × x = 76x 100 100 ⇒ 76 = 68,400 100 ⇒ x = 68,400 × 100 = 90,000 tonnes. 76
