Advertisements
Advertisements
Question
Choose the correct alternative answer for the following question .
In an A.P. first two terms are –3, 4 then 21st term is ...
Options
-143
143
137
17
Advertisements
Solution
It is given that,
a = –3
a2 = 4
We know that,
\[a_2 = a + \left( 2 - 1 \right)d\]
\[ \Rightarrow 4 = - 3 + d\]
\[ \Rightarrow d = 7\]
Now,
\[a_{21} = a + \left( 21 - 1 \right)d\]
\[ = - 3 + 20\left( 7 \right)\]
\[ = - 3 + 140\]
\[ = 137\]
APPEARS IN
RELATED QUESTIONS
Divide 32 into four parts which are in A.P. such that the product of extremes is to the product of means is 7 : 15.
The 7th term of the an AP is -4 and its 13th term is -16. Find the AP.
If an denotes the nth term of the AP 2, 7, 12, 17, … find the value of (a30 - a20 ).
Draw a triangle PQR in which QR = 6 cm, PQ = 5 cm and times the corresponding sides of ΔPQR?
The Sum of first five multiples of 3 is ______.
Two A.P.’s are given 9, 7, 5, ... and 24, 21, 18, ... If nth term of both the progressions are equal then find the value of n and nth term.
Rs 1000 is invested at 10 percent simple interest. Check at the end of every year if the total interest amount is in A.P. If this is an A.P. then find interest amount after 20 years. For this complete the following activity.
If the sum of a certain number of terms starting from first term of an A.P. is 25, 22, 19, ..., is 116. Find the last term.
Ramkali would need ₹1800 for admission fee and books etc., for her daughter to start going to school from next year. She saved ₹50 in the first month of this year and increased her monthly saving by ₹20. After a year, how much money will she save? Will she be able to fulfil her dream of sending her daughter to school?
Write the sum of first n odd natural numbers.
Q.3
Q.10
Find the sum of first 20 terms of an A.P. whose first term is 3 and the last term is 57.
Find whether 55 is a term of the A.P. 7, 10, 13,... or not. If yes, find which term is it.
In an A.P. (with usual notations) : given d = 5, S9 = 75, find a and a9
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 Sn denotes the sum of first n terms of an AP, prove that S12 = 3(S8 – S4)
Find the sum of all odd numbers between 351 and 373.
If the first term of an A.P. is 5, the last term is 15 and the sum of first n terms is 30, then find the value of n.
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.
