EXERCISE 10B
1. Rupesh secures 495 marks out of 750 in his annual examination Find the percentage of
2. The monthly salary of a typist is 15625. If he gets an increase of 12%, find his new salary
3. The excise duty on a certain item has been reduced to 760 from 950. Find the reduction
5. 70% of the students in a school are boys and the number of girls is 504. Find the number of
6. An ore contains 12% copper. How many kilograms of the ore are required to get 69 ks
percentage of pure gold in it
0 %
Hence, 22-carat gold 1
marks obtained by him.
per cent in the excise duty on that item.
10464. What is its total cost?
4. 96% of the cost of a TV is
of copper?
boys in the school.
on is
7. 36% of the maximum marking the maximuma marksst. A student gets 123 marks and
8. A fruit-seller had some apples. He sells 40% of them and still has 420 apples. Find
number of apples he had originally.
9. In an examination, 72% of the total examinees passed. If the number of failures is 392,
the total number of examinees.
10. After deducting a commission of 5%, a moped costs 2 15200. What is its gross value
11. Gunpowder contains 75% of nitre and 10% of sulphur, and the rest of it is charcoal,
the amount of charcoal in 8 kg of gunpowder.
12. Chalk contains 3% of carbon, 10% of calcium and 12% of oxygen. Find the amount in
of each of these substances in 1 kg of chalk.
Answers
Answer: 1. Maximum marks of the examination = 750
Marks secured by Rupesh = 495
Percentage of marks secured = (495750×100)% = 66%
Hence, Rupesh scored 66% in the examination.
2. Total monthly salary = Rs 15625
Increase percentage = 12%
∴ Amount increase = 12% of Rs 15625
= Rs (15625×12100) = Rs 1875
∴ New salary = Rs 15625 + Rs 1875 = Rs 17500
Hence, the new salary of the typist is Rs 17,500.
3. Original excise duty on the item = Rs 950
Amount reduced on excise duty = Rs (950 − 760) = Rs 190
∴ Reduction percent = (Reduction amount Original value×100)
= (190950×100) = 20
Hence, the excise duty on that item is reduced by 20%.
4. Let Rs x be the total cost of the TV set.
Now, 96% of the total cost of TV = Rs 10464
⇒ 96% of Rs x = Rs 10464
⇒ (96100×x) = 10464
∴ x = (10464×10096) = 10900
Hence, the total cost of the TV set is Rs 10900.
5. Let the total number of students be 100.
Then, number of boys = 70
∴ Number of girls = (100 − 70) = 30
Now, total number of students when the number of girls is 30 = 100
Then, total number of students when the number of girls is 504 = (10030×504) = 1680
∴ Number of boys = (1680 − 504) = 1176
Hence, there are 1176 boys in the school.
6. Let x kg be the amount of the required ore.
Then, 12% of x kg = 69 kg
⇒ (12100×x) kg = 69 kg
⇒ x = (69×10012) kg = 575 kg
Hence, 575 kg of ore is required to get 69 kg of copper.
7. Let x be the maximum marks.
Pass marks = (123 + 39) = 162
Then, 36% of x = 162
⇒ (36100×x)=162
⇒ x = (162×10036) = 450
8. Suppose that the fruit seller initially had 100 apples.
Apples sold = 40
∴ Remaining apples = (100 − 40) = 60
Initial amount of apples if 60 of them are remaining = 100
Initial amount of apples if 1 of them is remaining = (10060)
Initial amount of apples if 420 of them are remaining = (10060×420) = 700
Hence, the fruit seller originally had 700 apples.
9. Suppose that 100 candidates took the examination.
Number of passed candidates = 72
Number of failed candidates = (100 − 72) = 28
Total number of candidates if 28 of them failed = 100
Total number of candidates if 392 of them failed = (10028×392) = 1400
Hence, the total number of examinees is 1400.
10. Suppose that the gross value of the moped is Rs x.
Commission on the moped = 5%
Price of moped after deducting the commission = Rs ( x − 5% of x)
= Rs (x−5x100) = Rs (100x−5x100) = Rs (95x100)
Now, price of the moped after deducting the commission = Rs 15200
Then, Rs (95x100)= Rs 15200
∴ x = Rs (15200×10095) = Rs (160 × 100) = Rs 16000
Hence, the gross value of the moped is Rs 16000.
11. Total quantity of gunpowder = 8 kg = 8000 g (1 kg = 1000 g)
Quantity of nitre in it = 75% of 8000 g
= (75100×8000) g = 6000 g = 6 kg
Quantity of sulphur in it = 10% of 8000 g
= (10100×8000) g = 800 g = 0.8 kg
∴ Quantity of charcoal in it = {8000 − (6000 + 800)} g
= (8000 − 6800) g
= 1200 g = 1.2 kg
Hence, the amount of charcoal in 8 kg of gunpowder is 1.2 kg.
12. Total quantity of chalk = 1 kg = 1000 g
Now, we have the following:
Quantity of carbon in it = 3% of 1000 g
=(3100×1000) = 30 g
Quantity of calcium in it = 10% of 1000 g
= (10100×1000) g = 100 g
Quantity of oxygen in it = 12% of 1000 g
= (12100×1000) g = 120 g