# Important Questions for CBSE Class 11 Maths Chapter 9 - Sequences and Series

## CBSE Class 11 Maths Chapter-9 Important Questions - Free PDF Download

**4 Marks Questions**

**3.Find the sum to n terms of the series **

33 34

**Ans.**a_{n} = 1^{2} + 2^{2 }+ 3^{2} + --- +n^{2}

35 36

37 38

39 40

41 42

43 44

45 46

47 48

49 50

51

**4.Show that the sum of (m+n) ^{th} and (m-n)^{th} terms of an A. P. is equal to twice the m^{th} term. **

52 53

**Ans. **a_{m+n} = a + (m+n-1) d

54

**6 Marks Questions**

**1. 150 workers were engaged to finish a job in a certain no. of days 4 workers dropped out on the second day, 4 more workers dropped out on the third day and so on. It took 8 more days to finish the work find the no. of days in which the work was completed **

**Ans. **a = 150, d = -4

If total works who would have worked all n days 150(n-8)

**2. ****Prove that the sum to n terms of the series **

**Ans. **Sn = 11 + 103 + 1005 + ---- + n terms

Sn = (10+1) + (102 + 3) + (103 + 5) + ----- + [10n + (2n-1)]

**3. ****The ratio of A M and G. M of two positive no. a and b is m : n show that **

**Ans. **

Sq both side

**4. ****Between 1 and 31, m number have been inserted in such a way that the resulting sequence is an A.P. and the ratio of 7th and (m-1)th no. is 5:9 find the value of m.**

**Ans.**

**5. ****The Sum of two no. is 6 times their geometric mean, show that no. are in the ratio (3 + 3 ****√****2) : (3 – 2 ****√****2)**

**Ans.**