Question
In an arithmetic progression, the 4th term is 23 and the
9th term is 48. What is the sum of the first 20 terms?Solution
ATQ, Let first term = a, common difference = d. 4th term: a + 3d = 23 9th term: a + 8d = 48 Subtract: (a + 8d) − (a + 3d) = 48 − 23 5d = 25 ⇒ d = 5. Then a = 23 − 3d = 23 − 15 = 8. Sum of first 20 terms: Sₙ = n/2 [2a + (n − 1)d] S₂₀ = 20/2 [2·8 + 19·5] = 10 [16 + 95] = 10 × 111 = 1110.
In the question, assuming the given statements to be true, find which of the conclusion (s) among given three conclusions is/are definitely true and t...
In the question, assuming the given statements to be true, find which of the conclusion (s) among given three conclusions is /are definitely true and t...
Statements : C ≤ A < B ≤ D; E < B > F > G; I < H < G
Conclusions :
I. B > I
II. D > H
III. H < B
In the question, assuming the given statements to be true, find which of the conclusion (s) among given three conclusions is/are definitely true and the...
In the question, assuming the given statements to be true, find which of the conclusion (s) among given three conclusions is/are definitely true and th...
Statements: M > N = W; J < P = N; Y > P
Conclusions:
I. Y > W
II. M < Y
III. J > M
In the question, relationship between some elements is shown in the statements (s). These  statements are followed by two conclusions. Read the statem...
Statement: T > B = PÂ `>=` Â C ; BÂ `>=` Â J > F; OÂ `<=` Â JÂ `<=` Â CÂ Â Â Â
Conclusions:  I.  J < T    II. T > F
...Statements: R < S > T; U < V ≤ S; R > P
Conclusions:
I. S > P
II. U < R
III. T < P
Statements: Q @ X % Y % W; Y $ O $ B
Conclusions:
I. Â X % B
II. Q @ W
III. O $ X
...
