Latest TCS Aptitude Question SOLUTION: How many 7’s are there between 0 to 400?

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(#M40010748) TCS Numerical Ability question Keep an EYE

How many 7’s are there between 0 to 400?

Asked In TCS krishnamurthy (11 years ago)

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Manav  (11 years ago)

If u mean

How many 7s are there between 0 to 400?

From 0 to 100, there are 20 sevens.
7,17,27,37,47,57,67,70,71,72,73,74,75,76,77,78,79,87,97

From 0 to 400, there are 4*20 = 80 sevens.

Is this solution Helpfull? Yes (67) | No (20)  

SDeep Bhattacharya  (11 years ago)

Let us consider a general number (100A+10B+C)
Now, by problem A=0,1,2,3.
Now, consider the following cases:
1st case: WHEN B = 7 BUT C IS NOT EQUAL TO 7:
------------------------------------------------------
In this case A=0,1,2,3.
C=0,1,2,3,4,5,6,8,9.
So,in this case a total number= 4*9=45;

2nd Case: WHEN C = 7 BUT B IS NOT EQUAL TO 7:
--------------------------------------------------------
Now, also A=0,1,2,3
B=0,1,2,3,4,5,6,8,9
So, here also 4*9 = 36 cases.

So, for both the above cases
We get a total (36+36)=72 numbers each containing a 7 as one of its digits.

Now, 3rd Case : When B=7 & C=7:
-------------------------------------------
In this case A=0,1,2,3
B=7
C=7
So, total number of integers = 4
Now,note that in this case every integer contains two 7 [since B=C=7] .
So, total number of 7 in this 3rd case = 2*4 =8.

Now, clearly none of the above 3 cases ,overlaps with each other.

So, from 0 ----> 400 ,we get a total of (36+36+8)= 80 sevens..

So, 80 sevens are there between 0 to 400..

Thanks to all..:-):-)..

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ganesh  (11 years ago)

every 0-100 there are 9+10 sevens
9 for 0-67,80-100,
10 is for 70-79
so totally 19sevens/100
using this for 400=19*4=76 sevens only
76

Is this solution Helpfull? Yes (11) | No (42)  

SDeep Bhattacharya  (11 years ago)

Please mention the problem properly & clearly..

Is this solution Helpfull? Yes (5) | No (4)  

jimmykk  (11 years ago)

ans is 80. O-100 there are 20 7's accordind to this there are 80 7's between 0-400.

Is this solution Helpfull? Yes (5) | No (7)  

hima deepika S S  (11 years ago)

first find between 0 to 100,
it can be written as 00,01,02,03,......to 99... bcz, 100 do not have any 7's and it do not affect the number of 7's.... hence the total number of digits in 00 to 99 are 200.... consisting of 0 to 9 digits.. hence 200/10 = 20 digits of each type....( 0,1,2,3,4,5,6,7,8,9) hence 20 number of 7's.
similarly, from 100 to 200, - 20 7's
200 to 300 - 20
300 to 400 - 20
total= 80.

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Sagar Patil  (11 years ago)

in 1 to 100 thr r 20 7's ( any of 2 3 4 5 6 7 8 9)
so 0-400 80 7's

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tarun  (10 years ago)

400/7+400/49+400/343
57+8+1=66

value/n+value/n square+value/n cube 66 ans

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