Number System - Questions & Discussions

GOOD Morning :-P
6.how many 3 digit no:have the property tht their digit taken from left to right form an AP or GP

Taking case by case
1st for AP
1 the common difference can be -0,1,2,3,4
Hence possibilities are 111 123 135 147 159=5 cases
for 2 same way as 0,1,2,3 222 234 246 258 = 4 cases
for 3 333 345 357 369= 4cases
for 4 444 456 468 =3 cases
for 5 555 567 579=3 cases
for 6 666 678 =2 cases
for 7 777 789 = 2 cases
two cases for 8,9
total aps=25 aps are possible

For GPs with r=1 are same for all 1-9 hence we won't take that
let with r=2
124 248
And with r=3
139
Total cases 3

Hence net cases possible for AP or GP
=25+3
=28

Correct me if i am wrong
GOOD Morning :-P
1. Find 28383rd term in series 1234567891011..
a.3 b.4 c.9 d.7
2. sum of 1/1*5+1/5*9+1/9*13+..+1/221*225
a.28/221 b.56/221, c.56/225 d. none
3. sum of 1/(2^1/2+1^1/2)+1/(2^1/2+3^1/2)+..+1/(120^1/2+121^1/2)
a. 10 b.11 c.12 d.none
4. sum of infinite term 1/1+1/3+1/6+1/10+1/15.
a.2 b.2.25 c.3 d.4
5. sum of +1/6+1/12+1/20+..+1/156+1/182
6.how many 3 digit no:have the property tht their digit taken from left to right form an AP or GP


I was able to do the first three
1.a
2.c
3.a
For this i got the ans as 38
Taking case by case
1st for AP
1 the common difference can be -0,1,2,3,4
Hence possibilities are 111 123 135 147 159=5 cases
for 2 same way as 0,1,2,3 222 234 246 258 = 4 cases
for 3 333 345 357 369= 4cases
for 4 444 456 468 =3 cases
for 5 555 567 579=3 cases
for 6 666 678 =2 cases
for 7 777 789 = 2 cases
two cases for 8,9
total aps=25 aps are possible

For GPs with r=1 are same for all 1-9 hence we won't take that
let with r=2
124 248
And with r=3
139
Total cases 3

Hence net cases possible for AP or GP
=25+3
=28

Correct me if i am wrong

How did you solve the first question please explain.

GOOD Morning :-P
----------------
5. sum of +1/6+1/12+1/20+..+1/156+1/182
---------------

hi,
+1/6+1/12+1/20+..+1/156+1/182
can be written as
1 - 1/2 + 1/2 -1/3 + 1/3 -1/4 + 1/4 -1/5 + .... + 1/12 -1/13 + 1/13 - 1/14
which comes out to be
1 - 1/14
= 13/14
Taking case by case
1st for AP
1 the common difference can be -0,1,2,3,4
Hence possibilities are 111 123 135 147 159=5 cases
for 2 same way as 0,1,2,3 222 234 246 258 = 4 cases
for 3 333 345 357 369= 4cases
for 4 444 456 468 =3 cases
for 5 555 567 579=3 cases
for 6 666 678 =2 cases
for 7 777 789 = 2 cases
two cases for 8,9
total aps=25 aps are possible

For GPs with r=1 are same for all 1-9 hence we won't take that
let with r=2
124 248
And with r=3
139
Total cases 3

Hence net cases possible for AP or GP
=25+3
=28

Correct me if i am wrong

0 cant be taken as a common difference bro,,,
also for GPS..
u have common ratio of 2/3 and 3/2
in that case you have nos. like 964 and 469
with common ratio 1/3 we have nos. 962 and
with common ratio 1/2 we have 421, 842 etc...lot of gps are possible...thy'll be finite though:)
GOOD Morning :-P
-----------
4. sum of infinite term 1/1+1/3+1/6+1/10+1/15.
a.2 b.2.25 c.3 d.4
-----------

hi,
here the nth terms can be written as
1/(1+2+3+...+n)
= 2/n(n+1)
= 2
here the sum upto n terms of the series will be
= 2
so as n tends to infinity, the term 1/(n+1) will tend to 0...
hence the sum will become 2 = 2
hope it is correct...
SushantoCalatur Says
How did you solve the first question please explain.


1---9 there are 9 digits
10-99 there are 180 digits
100-999 --->2700 digits....

similarly we find the the remaining digits and find out total 4 digit number present...
the number will be 7371...here 2 will be 28381 digit..
28383rd digit will be 3...

it's option a ....
correct me if i'm wrong
GOOD Morning :-P
1. Find 28383rd term in series 1234567891011..
a.3 b.4 c.9 d.7
2. sum of 1/1*5+1/5*9+1/9*13+..+1/221*225
a.28/221 b.56/221, c.56/225 d. none
3. sum of 1/(2^1/2+1^1/2)+1/(2^1/2+3^1/2)+..+1/(120^1/2+121^1/2)
a. 10 b.11 c.12 d.none
4. sum of infinite term 1/1+1/3+1/6+1/10+1/15.
a.2 b.2.25 c.3 d.4
5. sum of +1/6+1/12+1/20+..+1/156+1/182
6.how many 3 digit no:have the property tht their digit taken from left to right form an AP or GP

1.
taking terms to be digits
option a
45 + 90*2 + 900*3 + 4x = 28383
x = 6364, rem = 2
7363 7364
28383rd digit = 3
2.
option c
sum = (1/4)
sum =(1/4)224/225 = 56/225
3.
option a
sum = root2 - root1 + root3 - root2 + root4 - root3 +.....+root121 - root120
sum = 11 - 1 = 10
4.
option a
nth term = 2/n(n+1) = 2
sum = 2
sum = 2
5.
nth term = 1/n(n+1) = 1/n - 1/n+1
sum = 1 - 1/14 = 13/14

6.
AP:-
abc
b = a+c/2
a+c = 2==>2
a+c = 4==>4
a+c = 6==>6
a+c = 8==>8
a+c = 10==>9
a+c = 12==>7
a+c = 14==>5
a+c = 16==>3
a+c = 18==>1
total = 45
GP:-
b = root(ac)
ac = 1==>1.......111
ac = 4==>3.......421,124,222
ac = 9==>3.......333,931,139
ac = 16==>3......444,842,248
ac = 25==>1......555
ac = 36==>3......666,964,469
ac = 49==>1......777
ac = 64==>1......888
ac = 81==>1......999
total = 17
common = 9
grand total = 53
1.
taking terms to be digits
option a
45 + 90*2 + 900*3 + 4x = 28383
x = 6364, rem = 2
7363 7364
28383rd digit = 3

explannation pls


1.
taking terms to be digits
option a
45 + 90*2 + 900*3 + 4x = 28383
x = 6364, rem = 2
7363 7364
28383rd digit = 3

1.
taking terms to be digits
option a
45 + 90*2 + 900*3 + 4x = 28383
x = 6364, rem = 2
7363 7364
28383rd digit = 3

explannation pls



Its actually 9+90*2+900*3+4x = 28383
=> x= 6373, rem = 2
6373 63. 28383rd digit is 3.

Hi all

Thanks for the detailed explanation . i will be back with some more problems 😃 later....

Anosh

p is a natural number,2p is having 28 divisors and 3p has 30 divisors.how many divisors of 6p will be there ?how to do such kind of questions?plzz explain.

destiny1400 Says
p is a natural number,2p is having 28 divisors and 3p has 30 divisors.how many divisors of 6p will be there ?how to do such kind of questions?plzz explain.


Let p= 2^a*3^b*5^c..... =>No. of factor of p=(a+1)(b+1)(c+1).... =F
2p= 2^(a+1)*3^b*5^c....=>.No. of factor of 2p=(a+2)(b+1)(c+1).... =28
3p= 2^a*3^(b+1)*5^c.....=>No. of factor of 3p=(a+1)(b+2)(c+1).... =30

6p= 2^(a+1)*3^(b+1)*5^c+....
No. of factor of 6p=(a+2)(b+2)(c+1)....
Put the value of (a+2)and (b+2) from the above eqns, u will get the answer
destiny1400 Says
p is a natural number,2p is having 28 divisors and 3p has 30 divisors.how many divisors of 6p will be there ?how to do such kind of questions?plzz explain.


28=4*7 thus it is in form 2p=2^6*3^3 thus p= 2^5*3^3 6p=2^6*3^4 thus total factor = 7*5= 35

i a+b+c=18
find the maximum value of a^3*b^2*c

destiny1400 Says
p is a natural number,2p is having 28 divisors and 3p has 30 divisors.how many divisors of 6p will be there ?how to do such kind of questions?plzz explain.



2p is having 28 divisors and 3p has 30 divisors

the above statement imples..

p has 24 factors { 6*4}


so 6p has 7*5 = 35 factors
i a+b+c=18
find the maximum value of a^3*b^2*c



i think answer is 49000

What is the digit at the hundredths place of the number N = 45^36 ?

(1) 1 (2) 0 (3) 6 (4) 5 (5) 7

2p is having 28 divisors and 3p has 30 divisors

the above statement imples..

p has 24 factors { 6*4}


so 6p has 7*5 = 35 factors


dude y r u not takin the fact 3p has 30 divisors?

wat if 3p had 24 factors or smthin else


will ur answer not change ?