Latest IBPS Aptitude Question SOLUTION: How many 1's are there between 100 to 1000?

0k now look into the cart right here where u will find how many ones are between 1 and 1000

0 to 9 = 1 (this indicates the number of 1s)

10 to 19 =1+10 (as all the digits got 1 in them like 11,12,13.....there are 10 digits with 1s in the left and 11 with a 1 in its right just like what we have seen in 0 to 9)

20 to 29 =1
30 to 39 =1
.....................
....................
90 to 99 =1
so except 10 to 19 (got 11 ones) we have got one 1 on 9 other occasions
so we find
0 to 99 = 11+(1.9)
=11 +9
=20


we shall also find 20 ones in the groups ( 200 to 299) ,(300 to 399) ,.,,,,,,,( 900 to 999) as they do not have extra ones in them .see: 91 ,291,391,491,991 .
so here we got 9 groups that got 20 ones in them
so except the group ( 100 to 199 ) the number of 1s between 1 and 999 is:
9.20
=180
the group 100 to 199 has got 100 number having an extra 1 each
so 100 to 199 = 20 +100
= 120
so from 1 to 999 we got (180 +120)=300 ones
1000 got one 1
so the total is 301
even a school going child will understand my explanation for sure.:D but if u still cant u can see the chart below

1 to 99 =20
100 to 199 =120
200 to 299 =20
300 to 399 =20
400 to 499 =20
500 to 599 =20
600 to 699 =20
...................( my hand is cramping :(
900 to 999 =20
1000 = 1
total=301

1001
on unit digit 1's come 10*10
on ten digit 1's come 10*10
on hundred digit 1's come 100
on thousand digit 1's come 1
so 100+100+100+1=1001

from 1-99:20
from 101-200:99 at 100th place
total=9*20+99=279

100+100+100+1=301