Advertisements
Advertisements
प्रश्न
There are 25 rows of seats in an auditorium. The first row is of 20 seats, the second of 22 seats, the third of 24 seats, and so on. How many chairs are there in the 21st row ?
Advertisements
उत्तर
The arrangement of chairs is 20, 22, 24, 26, ..........
Which is an A. P.
Here, a = 20, d = 2. We want to find t21.
tn = a + (n-1)d
∴ t21 = 20 + (21-1) × 2
= 20 + 40
= 60
∴ There are 60 chairs in the 21st row.
APPEARS IN
संबंधित प्रश्न
Ramkali required Rs 2,500 after 12 weeks to send her daughter to school. She saved Rs 100 in the first week and increased her weekly saving by Rs 20 every week. Find whether she will be able to send her daughter to school after 12 weeks.
What value is generated in the above situation?
The ratio of the sum use of n terms of two A.P.’s is (7n + 1) : (4n + 27). Find the ratio of their mth terms
Show that a1, a2,..., an... form an AP where an is defined as below:
an = 3 + 4n
Also, find the sum of the first 15 terms.
Find the sum of the following arithmetic progressions: 50, 46, 42, ... to 10 terms
Find the sum 25 + 28 + 31 + ….. + 100
If 10 times the 10th term of an AP is equal to 15 times the 15th term, show that its 25th term is zero.
The sum of three consecutive terms of an AP is 21 and the sum of the squares of these terms is 165. Find these terms.
The first term of an AP is p and its common difference is q. Find its 10th term.
Find the sum of the following APs:
2, 7, 12, 17, ... to 19 terms.
Find the 25th term of the AP \[- 5, \frac{- 5}{2}, 0, \frac{5}{2}, . . .\]
Write an A.P. whose first term is a and common difference is d in the following.
a = –3, d = 0
Divide 207 in three parts, such that all parts are in A.P. and product of two smaller parts will be 4623.
Find the A.P. whose fourth term is 9 and the sum of its sixth term and thirteenth term is 40.
If the seventh term of an A.P. is \[\frac{1}{9}\] and its ninth term is \[\frac{1}{7}\] , find its (63)rd term.
The first and the last terms of an A.P. are 7 and 49 respectively. If sum of all its terms is 420, find its common difference.
Sum of n terms of the series `sqrt2+sqrt8+sqrt18+sqrt32+....` is ______.
How many terms of the A.P. 27, 24, 21, …, should be taken so that their sum is zero?
If the numbers n - 2, 4n - 1 and 5n + 2 are in AP, then the value of n is ______.
How many terms of the AP: –15, –13, –11,... are needed to make the sum –55? Explain the reason for double answer.
If 7 times the seventh term of the AP is equal to 5 times the fifth term, then find the value of its 12th term.
