Selina Solutions Concise Maths Class 7 Chapter 8 Percent and Percentage Exercise 8D revolves around determining the percentage, which makes the exercise more interesting. Mathematics is a subject which involves numbers where one can play with them to arrive at a specific solution. Solving the exercise wise problems improves time management skills among students, which is important from the exam perspective. Students can download Selina Solutions Concise Maths Class 7 Chapter 8 Percent and Percentage Exercise 8D PDF, from the links which are given here.

## Selina Solutions Concise Maths Class 7 Chapter 8: Percent and Percentage Exercise 8D Download PDF

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#### Exercise 8D page: 101

**1. 28% of a number is 84. Find the number.**

**Solution:**

Consider x as the number

28% of x = 84

We can write it as

28/100 × x = 84

By further calculation

28x = 84 × 100

So we get

x = 300

**2. Every month, a man spends 72% of his income and saves ₹ 12,600. Find:**

**(i) his monthly income**

**(ii) his monthly expenses**

**Solution:**

Consider ₹ x as the total salary of the man

Amount spent by man = 72/100 × x

Amount saved by man = ₹ 12,600

(i) His monthly income

x = 72/100 x + 12600

By further calculation

x = (72x + 1260000)/ 100

So we get

100x – 72x = 1260000

28x = 1260000

Here

x = 1260000/28

x = 45000

(ii) His monthly expenses = 72/100 × 45000

So we get

= 72 × 450

= ₹ 32, 400

**3. 1800 boys and 900 girls appeared for an examination. If 42% of the boys and 30% of the girls passed, find**

**(i) number of boys passed**

**(ii) number of girls passed**

**(iii) total number of students passed**

**(iv) number of students failed**

**(v) percentage of students failed.**

**Solution:**

(i) Number of boys passed = 42/100 × 1800 = 756

(ii) Number of girls passed = 30/100 × 900 = 270

(iii) Total number of students passed = 756 + 270 = 1026

(iv) Number of students failed = (1800 + 900) – 1026

By further calculation

= 2700 – 1026

= 1674

(v) Percentage of students failed = 1674/2700 × 100 = 62%

**4. 6 ¼ % of a weight is 0.25 kg. What is 45% of this weight?**

**Solution:**

Consider x kg as the required weight

6 ¼/100 × x = 0.25

We can write it as

25/4 × 1/100 × x = 25/100

By further calculation

25x = 25 × 4 = 100

x = 100/25 = 4 kg

So 45% of this weight = 45/100 × 4 = 4/5 = 1.8 kg

**5. An alloy consists of 13 parts of copper, 7 parts of zinc and 5 parts of nickel. Find the percentage of copper in the alloy.**

**Solution:**

Here the sum of all parts = 13 + 7 + 5 = 25

Percentage of copper = 13/25 × 100 = 52%

Percentage of zinc = 7/25 × 100 = 28%

Percentage of nickel = 5/25 × 100 = 20%

**6. An ore contains 15% of iron. How much ore will be required to get 36 kg of iron?**

**Solution:**

Consider x kg as the amount of ore

15/100 × x = 36

We can write it as

15x = 3600

So we get

x = 3600/15 = 240 kg

**7. Find the number which when increased by 6% becomes 424.**

**Solution:**

Consider x as the required number

x + (6/100 × x) = 424

By further calculation

x + 3x/50 = 424

By taking LCM

(50x + 3x)/ 50 = 424

So we get

53x = 424 × 50

x = (424 × 50)/ 53

x = 400

**8. Find the number which when decreased by 15% becomes 1360.**

**Solution:**

Consider x as the required number

x – (15/100 × x) = 1360

By further calculation

x – 3x/20 = 1360

Taking LCM

(20x – 3x)/ 20 = 1360

So we get

17x = 1360 × 20

x = (1360 × 20)/ 17 = 1600

**9. The cost of an article decreased from ₹ 17,000 to 15,980. Find the percentage decrease.**

**Solution:**

Decreased cost of article = 17000 – 15980 = ₹ 1020

So the percentage of decrease = 1020/17000 × 100 = 6%

**10. Actual length of a rope is 22.5 m but it is wrongly measured as 21.6 m. Find the percentage error.**

**Solution:**

Error measured = 22.5 – 21.6 = 0.9 m

So the percentage of error = 9/10 × 1/22.5 × 100

We get

= 9/10 × 10/225 × 100

= 4%