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- Question
- Find the sum of all numbers, which are divisible by 8 between 200 to 400.?
Options- A. 7800
- B. 7600
- C. 7200
- D. 7900
- Correct Answer
- 7800
ExplanationThe least number between 200 and 400, which is divisible by 8 is 200. The last term less than 400, which is divisible by 8 is 400 .
? The series is 200, 208, 216,... , 400.
The number of terms in the AP is
(400 - 200/ 8) + 1 = 26
n = 26
d = 8
? Sum = n/2[2a + (n - 1) d]
= 26/2 [2x 200 + (26 -1) x 8]
= 13[400 + 200] = 7800 - 1. Find the value of 1 - 2 - 3 + 2 - 3 - 4 + 3 - 4 - 5 + ... + 100 terms .?
Options- A. -694
- B. -626
- C. -624
- D. -676 Discuss
- 2. What is the 11th term of the series 1, 8, 15, ...?
Options- A. 69
- B. 73
- C. 71
- D. 72 Discuss
- 3. The 9th term exceeds the fifth term of an AP by 32. The sum of the ninth and fifth terms is 114. Find the eight term of the AP.?
Options- A. 60
- B. 63
- C. 65
- D. 68 Discuss
- 4. What term of the AP 10, 8, 6, 4, .... is - 28?
Options- A. 15
- B. 18
- C. 19
- D. 20 Discuss
- 5. Find the 10th term of the AP 13, 8, 3, -2,.......?
Options- A. - 32
- B. - 64
- C. - 30
- D. - 13 Discuss
- 6. How many terms of the series -20, -16, -12, ... must be taken so that the sum is 120?
Options- A. 5
- B. 20
- C. 15
- D. 10 Discuss
- 7. Find the sum of even number below 1672 (including it).?
Options- A. 699831
- B. 699731
- C. 699832
- D. 699732 Discuss
- 8. Find the sum of even numbers below 281.?
Options- A. 19740
- B. 19750
- C. 19760
- D. 19730 Discuss
- 9. The sum to 12 terms of an AP is equal to the sum to 18 terms. What will be the sum to 30 terms for this series?
Options- A. 3
- B. 2
- C. 1
- D. 0 Discuss
- 10. The number of bacteria in a certain culture doubles every hour. If there were 50 bacteria present in the culture originally, how many bacteria will be born in 12th hour?
Options- A. 102460
- B. 120450
- C. 102400
- D. 120400 Discuss
Odd Man Out and Series problems
Search Results
Correct Answer: -626
Explanation:
The first 100 terms of this series is
(1 - 2 - 3) + (2 - 3 - 4) + ... + (33 - 34 - 35) + 34
The first 33 terms of the above series will given an AP as
-4, -5, -6, ... -36
? Answer = 33 x (-20 ) + 34 = - 626
Correct Answer: 71
Explanation:
This is an AP with a = 1 and d = 7
? 11th term = a + (n - 1) x d = 1 + (11 - 1) x 7
= 1 + 10 x 7 = 71
Correct Answer: 65
Explanation:
T9 = a + (9 - 1)d = a + 8d
T5 = a + (5 - 1)d = a + 4d
T9 - T5 = 32
? (a + 8d) - (a + 4d) = 32
? 4d = 32
? d = 8
T9 + T5 = (a + 8d) + (a + 4d)
= 2a + 12d
T9 + T5 = 114
? 114 = 2(a + 6d)
? a + 6d = 57
? T8 = a + 7d
= a + 6d + d
= 57 + 8 = 65
Correct Answer: 20
Explanation:
We have, a = 10 , d = (8 - 10) = -2, Tn = - 28
Tn = a + (n - 1)d
? -28 = 10 + (n - 1) x (- 2)
? -28 = 10 - 2n + 2
? 2n = 12 + 28
? 2n = 40
? n = 20
Correct Answer: - 32
Explanation:
In the given AP,
we have a = 13 , d = (8 - 13) = -5 and n = 10
Tn = a + (n - 1)d
T10 = 13 + (10 - 1) - 5
= 13 + 9 x (-5) = 13 - 45 = -32
Correct Answer: 15
Explanation:
Sn = 120, a = -20, d = 4
Sn = n/2[2a + (n - 1)d ]
? 120 = n/2 [2 x (-20) + (n - 1) x 4]
? 120 = -20n + 2(n -1)n
? 120 = -20n + 2n2 - 2n
? 120 = 2n2 - 22n
? 2n2 - 22n - 120 = 0
? n2-11n - 60 = 0
? n2 - 15n + 4n - 60 = 0
? n(n - 15) + 4(n - 15) = 0
? (n + 4) (n - 15) = 0
? n = -4 or 15
? n = 15
Correct Answer: 699732
Explanation:
Sum of even numbers = n/2[(n/2) + 1)] = (1672/2) x [(1672/2) + 1]
= 699732
Correct Answer: 19730
Explanation:
As, n is odd.
? Sum of even number = [(n - 1)/2 ] [ (n + 1 )/2]
= 280/2 x 282/2 = 19740
Correct Answer: 0
Explanation:
As, S12 = S18
So, S11 = S19
S10 = S20
S9 = S19
.........
.........
.........
S0 = S30
As, S0 = 0
So, S30 = 0
Correct Answer: 102400
Explanation:
The number of bacteria at any given time forms a GP whose terms are given by 50, 100, 200, ... where
a = 50, r = 100/50 = 2
Tn = arn -1
? T12 = 50(2)12 - 1
= 50 x (2)11
= 102400
So, the number of bacteria born in 12th hour is 102400.
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