av8a
As previously stated, LRC is defined as 99% MRC. MRC is almost unflyable - speed unstable. As well, any variation, fast or slow, means you lose range. Hence flying LRC is achievable and, if the target speed is between MRC and LRC planned range is achieved.
Assumed temperature method is a way of reducing thrust at t/o when there is sufficient performance margin. Using rated thrust costs in terms of engine life, hence it's desirable to use less than max thrust where safe.
Roughly, assumed temp means determining the highest OAT at which the a/c with the current TOW could legally t/o from a given runway. After deducting a few degrees for a margin the thrust to be set is determined by entering the books with the "assumed temp" and setting the resulting N1/EPR.