@guest: Re# 91771-0
RAC= Reservation Against Cancellation
Different trains have different no. of RAC seats depending on the class of travel - SL/3A/2A. 1A and CC do not have RAC.
it will be approx.8 per coach in SL (figures may change) In 2A/3A it is less.
If...
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a passenger has RAC booking, he can travel in the train. The passenger will be sharing the Side Lower Berth with some other passenger.
Depending upon vacancy and sequence, RAC passengers are allotted berths during journey. it is also possible, that a passenger will have to travel in RAC witout getting full berth for the entire journey.

@guest: Re# 91771-0
RAC means Reservation Against Cancellation!
An RAC ticket gets you on the train (A WL ticket doesn’t) and in your chosen class, but there’s a chance you could end up with just a seat.
A berth is split into 2 seats for 2 RAC ticket holders, if there’s any last minute cancellations, or if any quota allocations remain unsold, or if...
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any confirmed ticket holders are given a free upgrade (more later), an RAC ticket holder is given the empty berth, the other RAC ticket holder can then convert the 2 seats into a berth.