If a, b, c and d are replaced by four different digits from 1 to 9 , inclusive, then what's the largest possible value for a.bc + 0.d
The answer is \(9.87 + 0.6 = 10.47\).
a.bc + 0.d, obviously a is the biggest, so we choose a to be 9.
b must be the second biggest because b is in the .1s digits, so we choose it to be 8. However, Guest made a little mistake because 0.d must be the second or third biggest as it is also in the .1s digits, and lastly c is the smallest, but the biggest one we haven't picked yet.
Thus 9.86 + 0.7 or 9.76 + 0.8 would both be the biggest. As dolphinia got, it would be 10.56.