If 60% of a first order reaction was completed in 60 minutes, 50% of the same reaction would be completed in approximately

Answer 1

ln(No/N) = kt
Solve for k using 100 for No and 40 for N(i.e., if it was 60% completed and you started with 100, you would have 40 left.
Then ln(No/N) = kt again, use k from above and solve for t.