**Q : 3 **In the following APs, find the missing terms in the boxes :

(v)

Given AP series is
Here,
Now,
Now, we know that
Now,
And
And
And
Therefore, missing terms are 53,23,8,-7
AP series is 53,38,23,8,-7,-22

**Q : 3 **In the following APs, find the missing terms in the boxes :

(iv)

Given AP series is
Here,
Now, we know that
Now,
And
And
And
Therefore, missing terms are -2,0,2,4
AP series is -4,-2,0,2,4,6

**Q : 3 **In the following APs, find the missing terms in the boxes :

(iii)

Given AP series is
Here,
Now, we know that
Now,
And
Therefore, missing terms are and 8
AP series is

**Q : 3 **In the following APs, find the missing terms in the boxes :

(ii)

Given AP series is
Here,
Now,
Now, we know that
Now,
And
Therefore, missing terms are 18 and 8
AP series is 18,13,8,3

**Q : 3 **In the following APs, find the missing terms in the boxes :

(i)

**Q : 20 **In a potato race, a bucket is placed at the starting point, which is m from the first potato, and the other potatoes are placed 3 m apart in a straight line. There are ten potatoes in the line (see Fig. ).

** **A competitor starts from the bucket, picks up the nearest potato, runs back with it, drops it in the bucket, runs back to pick up the next potato, runs to the bucket to drop it in, and she continues in the same way until all the potatoes are in the bucket. What is the total distance the competitor has to run?

[**Hint** : To pick up the first potato and the second potato, the total distance (in metres) run by a competitor is ]

Distance travelled by the competitor in picking and dropping 1st potato
Distance travelled by the competitor in picking and dropping 2nd potato
Distance travelled by the competitor in picking and dropping 3rd potato
and so on
we can clearly see that it is an AP with first term (a) = 10 and common difference(d) = 6
There are 10 potatoes in the line
Therefore, total distance travelled by...

**Q : 19 ** logs are stacked in the following manner: logs in the bottom row, in the next row, in the row next to it and so on (see Fig. ). In how many rows are the logs placed and how many logs are in the top row?

As, the rows are going up, the no of logs are decreasing,
We can clearly see that 20, 19, 18, ..., is an AP .
and here
Let suppose 200 logs are arranged in 'n' rows,
Then,
Now,
case (i) n = 25
But number of rows can not be in negative numbers
Therefore, we will reject the value n = 25
case (ii) n = 16
Therefore, the number of rows in which 200 logs are arranged is equal...

**Q : 18 **A spiral is made up of successive semicircles, with centres alternately at and , starting with centre at , of radii as shown in Fig. . What is the total length of such a spiral made up of thirteen consecutive semicircles? (Take )

[**Hint** : Length of successive semicircles is with centres at respectively.]

From the above given figure
Circumference of 1st semicircle
Similarly,
Circumference of 2nd semicircle
Circumference of 3rd semicircle
It is clear that this is an AP with
Now, sum of length of 13 such semicircles is given by
Therefore, sum of length of 13 such semicircles is 143 cm

**Q : 17 ** In a school, students thought of planting trees in and around the school to reduce air pollution. It was decided that the number of trees, that each section of each class will plant, will be the same as the class, in which they are studying, e.g., a section of Class I will plant tree, a section of Class II will plant trees and so on till Class XII. There are three sections of each class. How many trees will be planted by the students?

First there are 12 classes and each class has 3 sections
Since each section of class 1 will plant 1 tree, so 3 trees will be planted by 3 sections of class 1.Thus every class will plant 3 times the number of their class
Similarly,
No. of trees planted by 3 sections of class 1 = 3
No. of trees planted by 3 sections of class 2 = 6
No. of trees planted by 3 sections of class 3 = 9
No. of trees...

**Q : 16 ** A sum of Rs is to be used to give seven cash prizes to students of a school for their overall academic performance. If each prize is Rs less than its preceding prize, find the value of each of the prizes.

It is given that
Each price is decreased by 20 rupees,
Therefore, d = -20 and there are total 7 prizes so n = 7 and sum of prize money is Rs 700 so
Let a be the prize money given to the 1st student
Then,
Therefore, the prize given to the first student is Rs 160
Now,
Let is the prize money given to the next 6 students
then,
Therefore, prize money given to 1 to 7 student...

**Q : 15 **A contract on construction job specifies a penalty for delay of completion beyond a certain date as follows: Rs for the first day, Rs for the second day, Rs for the third day, etc., the penalty for each succeeding day being Rs more than for the preceding day. How much money the contractor has to pay as penalty, if he has delayed the work by days?

It is given that
Penalty for delay of completion beyond a certain date is Rs for the first day, Rs for the second day, Rs for the third day and penalty for each succeeding day being Rs more than for the preceding day
We can clearly see that
200,250,300,..... is an AP with
Now, the penalty for 30 days is given by the expression
Therefore, the penalty for 30 days is 27750

**Q : 14 ** Find the sum of the odd numbers between and .

Odd number between 0 and 50 are
1,3,5,...49
This is an AP with
There are total 25 odd number between 0 and 50
Now, we know that
Therefore, sum of the odd numbers between and 625

**Q : 13 **Find the sum of the first multiples of .

First 15 multiples of 8 are
8,16,24,...
This is an AP with
Now, we know that
Therefore, sum of the first 15 multiple of 8 is 960

**Q : 12 **Find the sum of the first positive integers divisible by .

Positive integers divisible by 6 are
6,12,18,...
This is an AP with
Now, we know that
Therefore, sum of the first positive integers divisible by is 4920

**Q : 11 ** If the sum of the first terms of an AP is , what is the first term (that is )? What is the sum of first two terms? What is the second term? Similarly, find the rd, the th and the th terms

It is given that
the sum of the first terms of an AP is
Now,
Now, first term is
Therefore, first term is 3
Similarly,
Therefore, sum of first two terms is 4
Now, we know that
Now,
Similarly,

**Q : 10 **Show that form an AP where an is defined as below :

(ii)

Also find the sum of the first terms in each case.

It is given that
We will check values of for different values of n
and so on.
From the above, we can clearly see that this is an AP with the first term(a) equals to 4 and common difference (d) equals to -5
Now, we know that
Therefore, the sum of 15 terms is -465

**Q : 10 **Show that form an AP where an is defined as below :

(i)

Also find the sum of the first terms .

It is given that
We will check values of for different values of n
and so on.
From the above, we can clearly see that this is an AP with the first term(a) equals to 7 and common difference (d) equals to 4
Now, we know that
Therefore, the sum of 15 terms is 525

**Q : 9 ** If the sum of first terms of an AP is and that of terms is , find the sum of

first terms.

It is given that
Now, we know that
Similarly,
On solving equation (i) and (ii) we will get
a = 1 and d = 2
Now, the sum of first n terms is
Therefore, the sum of n terms is

**Q : 8 ** Find the sum of first terms of an AP whose second and third terms are and

respectively.

It is given that
And
Now,
Now, we know that
Therefore, there are 51 terms and their sum is 5610

**Q : 7 **Find the sum of first terms of an AP in which and nd term is .

It is given that
Now, we know that
Now, we know that
Therefore, there are 22 terms and their sum is 1661

- Previous
- Next

Exams

Articles

Questions