A four digit number is to be formed using the digits 1 to 7
All digits of the number are different and repetition is not
allowed.
1. How many such numbers can be formed ?
2. How many such numbers are divisible by 4 ?
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Answer Posted / iii
Answer 1:
At unit's place 7 possibilities r dere.
At ten's place 6,
At hundred's place 5,
At thousand's place 4.
Therefore, 7*6*5*4=840
Answer 2:
for any number to b divisible by 4, the last two digit must
b divisible by 4. Such 2 digit combinations possible are.....
12,16,24,32,36,52,56,64,72,76.
There are total 7 nos
out of which a 4 digit no is to be formed.
7 nos can be arranged in 7! and 4 digit no. can be formed
in 4*7! ways
At last two places, any one combination out of these 10 is
possible. For first two digits in the 4 digit number, the
possible combinations are 5*4=20
So there r 20*10=200 numbers divisible by 4.
| Is This Answer Correct ? | 2 Yes | 0 No |
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