Hi Narayana,
The below formula is working
=IF(G5<100,"A",IF(G5<500,"B",IF(G5<1000,"C",IF(G5>1000,"D"))))
even this too is working
=LOOKUP(G5,100*{0,1,5,10},{"A","B","C","D"})
Many thanks to all who has given the formula
however will brief you more
this is to find out the approver...