Question

abcd x 9 = dcba

Answer 1

9x(1000a+100b+10c+d)=1000d+100c+10b+a

999a+99b=999d+99c

ab=dc

Answer 2

abcdx9=dcba

=> (1000a+100b+10c+d)x9=1000d+100c+10b+a

=> 999a+99b=999d+99c

=> ab=cd

k nha