Latest TCS Aptitude Question SOLUTION: A person starts writing all 3 digits numbers. How many times had he written the digit 2

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A person starts writing all 3 digits numbers. How many times had he written the digit 2

Asked In TCS ATIQUR RAHMAN (10 years ago)

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Pritesh Saurav  (10 years ago)

when 2 at unit place, then no formed= 90;
when 2 at tens place, then no formed= 90;
when 2 at hundreds place, then no formed= 100;
total= 90+90+100= 280

Is this solution Helpfull? Yes (36) | No (4)  

annu kumari  (10 years ago)

280 times,
when 2 is at unit place then hundred and tens can be arranged in 9*10=90
when 2 is at tens place then hundred and tens can be arranged in 9*10=90
when 2 is at hundred place then tens and unit can be arranged in 10*10=100
so total is 280 ways

Is this solution Helpfull? Yes (13) | No   

sireesha  (10 years ago)

from 1 to 100 each digit will be 20 times i.e 2b
where b is the base here as it is decimal base is 10...
similarly 1 to 1000 it is 3b^2...
1 to 10000 it is 4b^3...
from these ans is 3b^2-2b=280

Is this solution Helpfull? Yes (7) | No   

ashish  (10 years ago)

number of nos that can be formed =9*10*10 =900
now, exclude 2 from set i.e. {0,1,3,4,5,6,7,8,9}
and form 3 digit no i.e. 648
so number of digits with 2 =900-248
i.e. 252
guys its the best I came up with , you could verify it with number of 2's b/w 11 & 100 and its 18

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ak  (10 years ago)

ans = 300.

Is this solution Helpfull? Yes (2) | No (7)  

naveen sharma  (10 years ago)

28on putting 2 on unit place we have 90
on putting 2 on tens place we have 90
on putting 2 on hundred place we have 100
total 280

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Guru Pranav  (10 years ago)

280

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laxman  (10 years ago)

supose 1 digit numbers 1b^0(b=10) 1*10^0=1
2 digit number 2b 2*10=20
3 digit number 3b^2 3*10^2=300

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parvez sajjad  (10 years ago)

@sireesha, thank u,your sol'n is perfect.

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Aditya Dutta  (10 years ago)

210
from 0-100 2 will be written 11times(02,12,22,32,42,52,62,72,82,92)...
this will be repeated for 9 times...
from 200-299, there are 100 two's extra in the hundred's place...hence total number of twos in all the digits from 200-299 is 100+11=111
hence total number of twos=9*11+111=210

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sarika kumari  (9 years ago)

the answer is 280....

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