Latest Elitmus Aptitude Question SOLUTION: How many three digit numbers can be formed in which if one digit is 3 then it must be follwed by 7 and repetetion of digits is not allowed

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(#M40157752) ELITMUS Numerical Ability question Keep an EYE

How many three digit numbers can be formed in which if one digit is 3 then it must be follwed by 7 and repetetion of digits is not allowed

Asked In Elitmus Samjukta Das (7 years ago)

Unsolved Read Solution (5)

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Hemanth sai  (7 years ago)

if 7 is to be followed by 3 , then the numbers will be either 37_ or _37.
for 37_ ,we have 370,371,372,374,375,376,378,379.
and for _37,we have 137,237,437,537,637,837,937.
therefore i think the answer is 15

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Jayant Gope  (7 years ago)

The question says that if one number is 3 then it must be followed by 7, It does not says that we must include 3 in our formation of three digit number. Thus,
Let's count the number of three digit numbers without having 3 in it -
i.e. 8 x 8 x 7 = 448

Now, let's count the number of three digit numbers having 3 in it and is followed by 7 -
This would include two arrangements -
1) 37_ (Total 8 arrangements can be done i.e. 370, 371, 372, 374, 375, 376, 378, 379).

2) _37 (Total 7 arrangements can be done i.e. 137, 237, 437, 537, 637, 837, 937).

Hence, total number of three digit numbers can be formed is 448+8+7 = 463.

Is this solution Helpfull? Yes (8) | No (4)  

SHAVALA NANDEESHWARUDU  (7 years ago)

_37==>137,237,437,537,637,837,937 (7 numbers)
37_==>370,371,372,374,375,376,378,379 (8 numbers)
Total numbers that can be formed are 15

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ROHIT YADAV  (7 years ago)

Read the question carefully it says if there is a 3 then it is followed by 7. You have left cases where there is no 3

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Digesh Singh Bisht  (1 year ago)

Ans is 463. We have to consider other numbers also. I have seen all solutions and most of them are considering only number containg 3 and 7. We should consider other numbers also.
Mr. Jayant Gope has given right solution.

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