Advertisements
Advertisements
प्रश्न
Find the sum of all 11 terms of an A.P. whose 6th term is 30.
उत्तर
Given, 6th term of A.P. = 30
or, a6 = 30
or, a + (6 – 1)d = 30
or, a + 5d = 30 ...(i)
Since, Sum of n terms of A.P. is Sn = `n/2[2a + (n - 1)d]`
∴ S11 = `11/2[2a + (11 - 1)d]`
= `11/2[2d + 10d]`
= `(11 xx 2)/2 [a + 5d]`
= 11 × 30 ...[From equation (i)]
= 330
APPEARS IN
संबंधित प्रश्न
Find the sum of the first 15 terms of each of the following sequences having the nth term as
bn = 5 + 2n
Is -150 a term of the AP 11, 8, 5, 2, ……?
Kargil’s temperature was recorded in a week from Monday to Saturday. All readings were in A.P. The sum of temperatures of Monday and Saturday was 5°C more than sum of temperatures of Tuesday and Saturday. If temperature of Wednesday was –30° celsius then find the temperature on the other five days.
The sum of first 9 terms of an A.P. is 162. The ratio of its 6th term to its 13th term is 1 : 2. Find the first and 15th term of the A.P.
The sum of first n terms of an A.P is 5n2 + 3n. If its mth terms is 168, find the value of m. Also, find the 20th term of this A.P.
There are 25 trees at equal distances of 5 metres in a line with a well, the distance of the well from the nearest tree being 10 metres. A gardener waters all the trees separately starting from the well and he returns to the well after watering each tree to get water for the next. Find the total distance the gardener will cover in order to water all the trees.
If 18th and 11th term of an A.P. are in the ratio 3 : 2, then its 21st and 5th terms are in the ratio
The first term of an AP is –5 and the last term is 45. If the sum of the terms of the AP is 120, then find the number of terms and the common difference.
If the first term of an AP is –5 and the common difference is 2, then the sum of the first 6 terms is ______.
Measures of angles of a triangle are in A.P. The measure of smallest angle is five times of common difference. Find the measures of all angles of a triangle. (Assume the measures of angles as a, a + d, a + 2d)
