Grade 12Algebra

The number of 6 digit numbers that can be made with the digits 1,2,3 and 4 and having exactly two pairs of digits, is

Abhiram nair

9 Years agoGrade 12

2 Answers

Nishant Vora

Approved Tutor Answer9 Years ago

exactly two pairs means we can pair 1,2 with 3,4 and so on

Hence, 2 pairs = 4 numbers

hence all 4 numbers should be included

so number of 6 digit numbers which can be formed by using thedigits 1,2,3 and 4.

4^6

Lavya

7 Years ago

Choose the repeat digits from {1,2,3,4} in C(4,2) ways then the remaining two digits take care of themselves since we are not allowed any more pairs.
Now we have 6 numbers with 2 pairs and 2 singles which may be permuted in 6!/(2!2!1!1!) ways:

C(4,2)*6!/(2!2!1!1!) = 1080