Advertisements
Advertisements
प्रश्न
Find the sum of first 20 terms of the following A.P. : 1, 4, 7, 10, ........
Advertisements
उत्तर
Let a be the first term and d be the common difference of the given A.P. Then, we have a = 1 and d = 3.
We have to find the sum of 20 terms of the given A.P.
Putting a = 1, d = 3, n = 20 in
`S_n = \frac{n}{ 2 } [2a + (n - 1) d]`
∴ `S_20 = \frac {20}{2} [2 × 1 + (20 - 1) × 3]`
= 10 (2 + 57)
= 10 × 59
= 590
APPEARS IN
संबंधित प्रश्न
Find the sum of the first 22 terms of the A.P. : 8, 3, –2, ………
Is 184 a term of the AP 3, 7, 11, 15, ….?
Determine the nth term of the AP whose 7th term is -1 and 16th term is 17.
How many two-digits numbers are divisible by 3?
In an A.P. sum of three consecutive terms is 27 and their product is 504, find the terms.
(Assume that three consecutive terms in A.P. are a – d, a, a + d).
If the 9th term of an A.P. is zero then show that the 29th term is twice the 19th term?
If first term of an A.P. is a, second term is b and last term is c, then show that sum of all terms is \[\frac{\left( a + c \right) \left( b + c - 2a \right)}{2\left( b - a \right)}\].
The common difference of the A.P.
Kanika was given her pocket money on Jan 1st, 2008. She puts Rs 1 on Day 1, Rs 2 on Day 2, Rs 3 on Day 3, and continued doing so till the end of the month, from this money into her piggy bank. She also spent Rs 204 of her pocket money, and found that at the end of the month she still had Rs 100 with her. How much was her pocket money for the month?
The sum of the 4th and 8th term of an A.P. is 24 and the sum of the 6th and 10th term of the A.P. is 44. Find the A.P. Also, find the sum of first 25 terms of the A.P.
