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Exercise 12.4 - Chapter 12 Algebraic Expressions class 7 ncert solutions Maths - SaraNextGen [2024]


Question 1:

Observe the patterns of digits made from line segments of equal length. You will find such segmented digits on the display of electronic watches or calculators.

(a)

https://img-nm.mnimgs.com/img/study_content/curr/1/7/3/42/1676/Chapter%2012_html_2e6e3335.jpg

(b)

https://img-nm.mnimgs.com/img/study_content/curr/1/7/3/42/1676/Chapter%2012_html_6e863c99.jpg

(c)

https://img-nm.mnimgs.com/img/study_content/curr/1/7/3/42/1676/Chapter%2012_html_m7deb739b.jpg

If the number of digits formed is taken to be n, the number of segments required to form n digits is given by the algebraic expression appearing on the right of each pattern.

How many segments are required to form 5, 10, 100 digits of the kind −

https://img-nm.mnimgs.com/img/study_content/curr/1/7/3/42/1676/Chapter%2012_html_72b1af8c.jpg  , https://img-nm.mnimgs.com/img/study_content/curr/1/7/3/42/1676/Chapter%2012_html_m6666eacf.jpg  , https://img-nm.mnimgs.com/img/study_content/curr/1/7/3/42/1676/Chapter%2012_html_m2fce33ee.jpg .

Answer:

(a) It is given that the number of segments required to form n digits of the kind

https://img-nm.mnimgs.com/img/study_content/curr/1/7/3/42/1676/Chapter%2012_html_72b1af8c.jpg  is (5n + 1).

Number of segments required to form 5 digits = (5 × 5 + 1)

= 25 + 1 = 26

Number of segments required to form 10 digits = (5 × 10 + 1)

= 50 + 1 = 51

Number of segments required to form 100 digits = (5 × 100 + 1)

= 500 + 1 = 501

(b) It is given that the number of segments required to form n digits of the kind https://img-nm.mnimgs.com/img/study_content/curr/1/7/3/42/1676/Chapter%2012_html_m6666eacf.jpg  is (3n + 1).

Number of segments required to form 5 digits = (3 × 5 + 1)

= 15 + 1 = 16

Number of segments required to form 10 digits = (3 × 10 + 1)

= 30 + 1 = 31

Number of segments required to form 100 digits = (3 × 100 + 1)

= 300 + 1 = 301

(c)It is given that the number of segments required to form n digits of the kind https://img-nm.mnimgs.com/img/study_content/curr/1/7/3/42/1676/Chapter%2012_html_m2fce33ee.jpg  is (5n + 2).

Number of segments required to form 5 digits = (5 × 5 + 2)

= 25 + 2 = 27

Number of segments required to form 10 digits = (5 × 10 + 2)

= 50 + 2 = 52

Number of segments required to form 100 digits = (5 × 100 + 2)

= 500 + 2 = 502

Question 2:

Use the given algebraic expression to complete the table of number patterns.

S. No

Expression

Terms

1st

2nd

3rd

4th

5th

10th

100th

(i)

2n − 1

1

3

5

7

9

19

(ii)

3n + 2

2

5

8

11

(iii)

4n + 1

5

9

13

17

(iv)

7n + 20

27

34

41

48

(v)

n2 + 1

2

5

10

17

10, 001

Answer:

The given table can be completed as follows.

S.No.

Expression

Terms

1st

2nd

3rd

4th

5th

10th

100th

(i)

2n − 1

1

3

5

7

9

19

199

(ii)

3n + 2

2

5

8

11

17

32

302

(iii)

4n + 1

5

9

13

17

21

41

401

(iv)

7n + 20

27

34

41

48

55

90

720

(v)

n2 + 1

2

5

10

17

26

101

10,001-

Also Read : Exercise-13.1-Chapter-13-Exponents-&-Powers-class-7-ncert-solutions-Maths

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