Math, asked by tejasavinash59, 5 months ago

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EXERCISE 10B
1. Rupesh secures 495 marks out of 750 in his annual examination. Find the percentage of
marks obtained by him.
the monthly salary of a typist is 3 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 1950. Find the reduction
per cent in the excise duty on that item.
496% of the cost of a TV is 10464. What is its total cost?
70% of the students in a school are boys and the number of girls is 504. Find the number of
boys in the school
6. An ore contains 12% copper. How many kilograms of the ore are required to get 69 kg
of copper?
36% of the maximum marks are required to pass a test. A student gets 123 marks and is
declared failed by 39 marks. Find the maximum marks
(8. A)fruit-seller had some apples. He sells 40% of them and still has 420 apples. Find the
number of apples he had originally.
9. In an examination, 72% of the total examinees passed. If the number of failures is 392, find
the total number of examinees.
10. After deducting a commission of 5%, a moped costs 15200. What is its gross value?
11. Gunpowder contains 75% of nitre and 10% of sulphur, and the rest of it is charcoal. Find
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 grams
• of each of these substances in 1 kg of chalk.​

Answers

Answered by Darika25
3

Answer:

1.) Rupesh secures 495 marks out of 750 in his annual examination. Find the percentage of marks obtained by him.

Answer:

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.

Question 2:

The monthly salary of a typist is Rs 15625. If he gets an increase of 12%, find his new salary.

Answer:

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.

The excise duty on a certain item has been reduced to Rs 760 from Rs 950. Find the reduction per cent in the excise duy on that item.

3.)Answer:

Original excise duty on the item = Rs 950

Amount reduced on excise duty = Rs (950 − 760) = Rs 190

∴ Reduction percent = (Reduction amountOriginal value×100)

= (190950×100) = 20

Hence, the excise duty on that item is reduced by 20%.

Question 4:

96% of the cost of a TV is Rs 10464. What is its total cost?

its total cost?

ANSWER:

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.

Page No 147:

Question 5:

70% of the students in a school are boys and the number of girls is 504. Find the number of boys in the school.

ANSWER:

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.

Page No 147:

Question 6:

An ore contains 12% copper. How many kilograms of the ore are required to get 69 kg of copper?

ANSWER:

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.

Page No 147:

Question 7:

36% of the maximum marks are required to pass a test. A student gets 123 marks and is declared failed by 39 marks. Find the maximum marks.

ANSWER:

Let x be the maximum marks.

Pass marks = (123 + 39) = 162

Then, 36% of x = 162

⇒ (36100×x)=162

⇒ x = (162×10036) = 450

∴ Maximum marks = 450

Page No 147:

Question 8:

A fruit-seller had some apples. He sells 40% of them and still has 420 apples. Find the number of apples he had originally.

ANSWER:

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.

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Question 9:

In an examination, 72% of the total examinees passed. If the number of failures is 392, find the total number of examinees.

ANSWER:

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.

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Question 10:

After decuting a commission of 5%, a moped costs Rs 15200. What is its gross value?

ANSWER:

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.

Page No 147:

Question 11:

Gunpowder contains 75% of nitre and 10% of sulphur, and the rest of it is charcoal. Find the amount of charcoal in 8 kg of gunpowder.

ANSWER:

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.

Page No 147:

Question 12:

Chalk contains 3% of carbon, 10% of calcium and 12% of oxygen. Find the amount in grams of each of these substances in 1 kg of chalk.

ANSWER:

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

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