10th Maths 5.2

Chapter 5

Arithmetic Progressions

Like, Share, and Subscribe.

NCERT Class 10th solution of Exercise 5.1

Exercise 5.2

Q1. Fill in the blanks in the following table, given that a is the first term, d the common difference and an the nth term of the AP ;

 

 a

 d

 n

 an

 i)

 7

 3

 8

 ......

 ii)

 -18

 .....

 10

 0

 iii)

 .....

 -3

 18

 -5

 iv)

 -18.9

 2.5

 .....

 3.6

v)

 3.5

 0

 105

 .....

Sol. :
i)
an=a+(n-1)×d
an=7+(8-1)×3
an=7+7×3
an=7+21
an=28
Answer :
an=28
ii)
an=a+(n-1)×d
0=-18+(10-1)×d
0=-18+9×d
9d=18
d=2
Answer :
d=2.
iii)
an=a+(n-1)×d
-5=a+(18-1)(-3)
-5=a+17(-3)
-5=a-51
a=46
Answer :
a=46.
iv)
an=a+(n-1)×d
3.6=-18.9+(n-1)×2.5
3.6=-18.9+2.5n-2.5
3.6=-21.4+2.5n
2.5n=-21.4-3.6
n=-25.02.5
n=-10
Answer :
n=-10.
v)
an=a+(n-1)×d
an=3.5+(105-1)×0
an=3.5+0
an=3.5
Answer :
an=3.5.
Q2. Choose the correct choice is the following and justify :
i) 30th term of the AP : 10,7,4,...is
A) 97    B) 77    C) -77    D) -87
ii) 11th term of the AP : -3,-12,2,....is :
A) 28    B) 22    C) -38    D) -4812
Sol. :
i) Given : a=10,d=-3, and n=30
an=a+(n-1)d
a10=10+(30-1)(-3)
a10=10+29(-3)
a10=10-87
a10=-77
Answer :
(C).
ii) Given :a=-3,d=212, and n=11
an=a+(n-1)d
a11=-3+(11-1)(52)
a11=-3+25
a11=22
Answer :
(B).
Q3. In the following APs, find the missing terms in the boxes :
i) 2,,26
ii) ,13,,3
iii) 5,,,912
iv) -4,,,,,6
v) ,38,,,,-22
Sol. :
i)  Given : a1=2,a3=26, and n=1,3
an=a+(n-1)d
26=2+(3-1)d
26=2+2d
26-2=2d
24=2d
d=242
d=12
a2=2+(2-1)12
a2=2+12
a2=14
Answer :
d=12,2=12
ii) Given : a2=13,a4=3, and n=2,4
an=a+(n-1)d
13=a+(2-1)d
13=a+d_________(1)
3=a+(4-1)d
3=a+3d___________(2)
By equation (1) - (2)
13-3=a+d-(a+3d)
10=a+d-a-3d
10=(-2)d
d=-102
d=-5
Put in (1)
a+(-5)=13
a=18
a3=18+(3-1)(-5)
a3=18+2(-5)
a3=18-10
a3=8
Answer :
1=18,3=8.
iii) Given : a1=5,a4=912=9.5, and n=4
an=a+(n-1)d
9.5=5+(4-1)d
9.5-5=3d
4.5=5d
d=4.55
d=1.5
a2=a+(n-1)d
a2=5+(2-1)1.5=6.5
a3=a+(n-1)d
a3=5+(3-1)1.5=8
Answer :
2=6.5,3=8
iv) Given : a=-4,a6=6, and n=6
an=a+(n-1)d
a6=-4+(6-1)d
6=-4+5d
6+4=5d
10=5d
d=105
d=2
a2=-4+(2-1)2=-4+2=-2
a3=-4+(3-1)2=-4+4=0
a4=-4+(4-1)2=-4+6=2
a5=-4+(5-1)2=-4+8=4
Answer :
2=-2,3=0,4=2,and5=4.
v) Given : a2=38,a6=-22, and n=2,6
an=a+(n-1)d
38=a+(2-1)d
38=a+d_________(1)
-22=a+(6-1)d
-22=a+5d________(2)
By equation (2) - (1)
-22-38=a+5d-(a+d)
-60=a+5d-a-d
-60=4d
d=-604=-15
Put in equation (1)
38=a+(-15)
38=a-15
a=38+15=53
a3=53+(3-1)(-15)=53-30=23
a4=53+(4-1)(-15)=53-45=8
a5=53+(5-1)(-15)=53-60=-7
Answer :
1=53,3=23,4=8, and 5=-7.
Q4. Which term of the AP: 3,8,18, ...., is 78?
Sol. 
Given: a=3,d=8-3=5, and an=78
an=a+(n-1)d
78=3+(n-1)(5)
78=3+5n-5
78=-2+5n
5n=78+2
5n=80
n=805
n=16
Answer :
n=16.
Q5. Find the number of terms in each of the following APs :
i) 7,13,19,...,205    ii) 18,1515,13,....-47
Sol. :
i) Give: a=7,d=13-7=6, and an=205
an=a+(n-1)d
205=7+(n-1)(6)
205=7+6n-6
205=1+6n
6n=205-1
6n=204
n=2046
n=34
Answer :
n=34.
ii) Given: a=18,d=1512-1=312-1=15.5-81=-2.5, and an=-47
an=a+(n-1)d
-47=18+(n-1)(-2.5)
-47=18-2.5n+2.5
-47=20.5-2.5n
2.5n=47+20.5
2.5n=67.5
n=67.52.5
n=67525
n=27
Answer :
n=27.
Q6. Check whether -150 is a term of the AP: 11,8,5,2....  .
Sol. : Given: a=11,d=8-11=-3, and an=-150
an=a+(n-1)d
-150=11+(n-1)(-3)
-150=11-3n+3
-150=14-3n
3n=14+150
3n=164
n=1643
n=5423[ it is not natural number ]
Answer :
No, -150 is not a term of given AP.
Q7. Find the 31st term of an AP whose 11th term is 38 and the 16th term is 73.
Sol. : 
Given: a11=38,a16=73, and n=11,16
an=a+(n-1)d
38=a+(11-1)d
38=a+10d___________(1)
73=a+(16-1)d
73=a+15d___________(2)
By equation (2) - (1)
73-38=a+15d-(a+10d)
35=a+15d-a-10d
35=5d
d=355
d=7
Put in equation (1)
38=a+10(7)
38=a+70
a=-70+38
a=-32
Now 
a31=a+(30-1)d
a31=-32+30(7)
a31=-32+210
a31=178
Answer :
a31=178.
Q8. An AP consists of 50 terms of which 3rd term is 12 and the last term is 106. Find the 29th term.
Sol. : 
Given: a3=12,a50=106 and n=12,50
an=a+(n-1)d
12=a+(3-1)d
12=a+2d________________(1)
106=a+(50-1)d
106=a+49d______________(2)
By equation (2) - (1)
106-12=a+49d-(a+2d)
94=a+49d-a-2d
94=49d-2d
94=47d
d=9447
d=2
Put in equation (1)
12=a+2(2)
12=a+4
a=8
a29=a+(29-1)d
a29=8+28(2)
a29=8+56
a29=64
Answer :
a29=64.
Q9. If the 3rd and the 9th terms of an AP are 4 and -8 respectively, which term of this AP is zero.
Sol. : 
Given: a3=4,a9=-8, and an=0
an=a+(n-1)d
4=a+(3-1)d
4=a+2d______________(1)
-8=a+(9-1)d
-8=a+8d______________(2)
By equation (2) - (1)
-8-4=a+8d-(a+2d)
-12=a+8d-a-2d
-12=6d
d=-126
d=-2
Put in equation (1)
4=a+2(-2)
4=a-4
a=8
Now
an=8+(n-1)(-2)
0=8-2n+2
0=10-2n
2n=10
n=102
n=5
Answer :
n=5.
Q10. The 17th term of an AP exceeds its 10th term by 7. Find the common difference.
Sol. : 
According to question
a17-a10=7
a+(17-1)d-(a+(10-1)d=7
a+16d-a-9d=7
7d=7
d=77
d=1
Answer :
d=1.
Q11. Which term of the AP: 3,15,27,39,... will be 132 more than its 54th term?
Sol. :
Given: a=3,d=15-3=12
According to question
an-a54=132
a+(n-1)d-[a+(54-1)d]=132
3+(n-1)12-[3+53(12)]=132
3+12n-12-3-636=132
12n=132+636+12
12n=780
n=78012
n=65
Answer :
65th term.
Q12. Two APs have the same command difference. The difference between their 100th term is 100, what is the difference between their 1000th  terms?
Sol. : 
Let first term of first AP is a,
and first term of second AP is b.
According to question
a100-b100=100
a+(100-1)d-[b+(100-1)d]=100
a+99d-b-99d=100
`a-b=100___________________(1)
Now 
a1000-b1000
=a+(1000-1)d-[b+(1000-1)d]
=a+999d-b-999d
=a-b
from equation (1)
a-b=100
Answer :
The difference between 1000th terms will also be 100.
Q13. How many three-digit numbers are divisible by 7?
Sol. :
AP is 105,112,119,.......994.
where a=105,d=7, and an=994
an=a+(n-1)d
994=105+(n-1)7
994=105+7n-7
994=98+7n
7n=994-98
7n=896
n=8967
n=128
Answer :
n=128.
Q14. How many multiples of 4 lie between 10 and 250?
Sol. :
AP is 12,16,20,24,.....248
where a=12,d=4, and an=248
an=a+(n-1)d
248=12+(n-1)4
248=12+4n-4
248=8+4n
4n=248-8
4n=240
n=2404
n=60
Answer :
n=60.
Q15. For what value of n, are the nth terms of two APs: 63,65,67,....and `3, 10, 17,..... equal?
Sol. :
AP `63, 65, 67,.....
where a=63,d=65-63=2
AP `3, 10, 17, ....
where a=3,d=10-3=7
According to question
an=bn
63+(n-1)2=3+(n-1)7
63+2n-2=3+7n-7
7n-2n=63-3-2+7
5n=65
n=655
n=13
Answer :
n=13.
Q16. Determine the AP whose third term is 16 and the 7th term exceeds the 5th term by 12.
Sol. :
Let the AP is a,a+d,a+2d,.....
According to question
a3=a+2d
16=a+2d________(1)
and 
a7-a5=12
a+(7-1)d-[a+(5-1)d]=12
a+6d-a-4d=12
2d=12
d=6
Put in equation (1)
16=a+2(6)
16=a+12
a=4
a2=4+(2-1)6=4+6=10
a3=4+(3-1)6=4+12=16
a4=4+(4-1)6=4+18=22
Answer :
The AP is 4,10,16,22,......
Q17. Find the 20th term from the last term of the AP: 3,8,13,....,253.
Sol. :
By the given AP take in decending order
253,248,......,8,3
where a=253,d=248-253=-5
a20=253+(20-1)(-5)
a20=253+19(-5)
a20=253-95
a20=158
Answer :
a20=158.
Q18. The sum of the 4th and 8th terms of an AP is 24 and the sum of the 6th and 10th term is 44. Find the first three terms of the AP.
Sol. :
Let the AP is a, a+d,a+2d,......
According to question 
a4+a8=24
a+(4-1)d+a+(8-1)d=24
a+3d+a+7d=24
2a+10d=24
a+5d=12______________(1)
and
a6+a10=44
a+(6-1)d+a+(10-1)d=44
a+5d+a+9d=44
2a+14d=44
a+7d=22_____________(2)
By equation (2) - (1)
a+7d-(a+5d)=22-12
a+7d-a-5d=10
2d=10
d=102
d=5
Put in equation (1)
a+5(5)=12
a+25=12
a=-13
a2=-13+(2-1)5=-13+5=-8
a3=-13+(3-1)5=-13+10=-3
Answer :
The first three terms of AP is -13,-8,-3,.....
Q19. Subba Rao started work in 1995 at an annual salary of 5000 and received an increment of 200 each year. In which year did his income reach 7000?
Sol. :
Given: a=5000,d=200, and an=7000.
an=a+(n-1)d
7000=5000+(n-1)200
7000=5000+200n-200
200n=7000-5000+200
`n=2200/200
n=11
Answer :
11th year.
Q20. Ramkali served 5 in the first week of a year and then increased her weekly savings by 1.75. in the nth week, her weekly saving become 20.75, find n.
Sol. :
Given: a=5,d=1.75 and an=20.75
an=a+(n-1)d
20.75=5+(n-1)1.75
20.75=5+1.75n-1.75
1.75n=20.75-5+1.75
n=17.501.75
n=10
Answer :
10th year.

Comments

Popular posts from this blog

10th Maths Chapter 1

CBSE 10th and 12th Result

RSKMP 5th & 8th Result