TS EAMCET 6-Aug-2021 Shift 1 Question Paper

Since, the largest digit is in the middle, the middle digit is greater than or equal to 5 , the number of numbers with 5 in the middle =‌4P4
( ∵ the four places are to be filled by 1,2,3,4 )
Similarly, the number of numbers with 6 in the middle =‌5P4
The number of numbers with 7 in the middle =‌6P4
The number of numbers with 8 in the middle =‌7P4
The number of numbers with 9 in the middle =‌8P4
∴ Total number of such numbers
=‌4P4+‌5P4+‌6P4+‌7P4+‌8P4=

8

∑

r=4

‌rP4