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
Find the sum given below:
`7 + 10 1/2 + 14 + ... + 84`
In an AP given a3 = 15, S10 = 125, find d and a10.
If the 10th term of an AP is 52 and 17th term is 20 more than its 13th term, find the AP.
The 9th term of an AP is –32 and the sum of its 11th and 13th terms is –94. Find the common difference of the AP.
Find the value of x for which the numbers (5x + 2), (4x – 1) and (x + 2) are in AP.
Show that (a – b)2, (a2 + b2) and (a2 + b2) are in AP.
What is the sum of first 10 terms of the A. P. 15,10,5,........?
Find the sum \[7 + 10\frac{1}{2} + 14 + . . . + 84\]
In an A.P. the first term is 8, nth term is 33 and the sum to first n terms is 123. Find n and d, the common differences.
If the sum of three consecutive terms of an increasing A.P. is 51 and the product of the first and third of these terms is 273, then the third term is
The common difference of the A.P. is \[\frac{1}{2q}, \frac{1 - 2q}{2q}, \frac{1 - 4q}{2q}, . . .\] is
The term A.P is 8, 10, 12, 14,...., 126 . find A.P.
Which term of the AP 3, 15, 27, 39, ...... will be 120 more than its 21st term?
If the second term and the fourth term of an A.P. are 12 and 20 respectively, then find the sum of first 25 terms:
What is the sum of an odd numbers between 1 to 50?
A merchant borrows ₹ 1000 and agrees to repay its interest ₹ 140 with principal in 12 monthly instalments. Each instalment being less than the preceding one by ₹ 10. Find the amount of the first instalment.
If the first term of an A.P. is p, second term is q and last term is r, then show that sum of all terms is `(q + r - 2p) xx ((p + r))/(2(q - p))`.
In a ‘Mahila Bachat Gat’, Kavita invested from the first day of month ₹ 20 on first day, ₹ 40 on second day and ₹ 60 on third day. If she saves like this, then what would be her total savings in the month of February 2020?
The nth term of an Arithmetic Progression (A.P.) is given by the relation Tn = 6(7 – n)..
Find:
- its first term and common difference
- sum of its first 25 terms
The sum of 41 terms of an A.P. with middle term 40 is ______.
