It is to be noted that at inception of the Group Representation Constituencies (GRCs) system of elections in 1988, minority races were granted 13 guaranteed parliamentary seats through 13 GRCs where in at least one MP out of 3 forming each GRC had to be of a minority race- a total of 81 seats were contested that year with 42 under the category of single member constituencies and the rest (39) under the category of 'GRC'. The guaranteed parliamentary minority representation that year was thus 13/81 = 16.0494% of all parliamentary seats. Based upon the then non-Chinese population of 21.7%, the mandatory minority representation in 1988 was 16.049/21.7 = 73.960%.

By 2011 however, expansions in the size of each GRC, double in some cases, had increased to an average of 5 MPs per GRC, this without any proportionate increase in the numbers of minority MPs mandated per GRC.

It is duly noted that by 2010, the non-Chinese (minority races) population had since grown to 25.9% (increase by almost 20% cf 1980 figures). Using the 1988 formula of having 73.960% of the minority population enjoy mandated parliamentary representation, correcting for an 87 seat parliament, there would then be a need for 73.960% * 25.9% * 87 = 16.6654 minority MPs.

Even using a rounded up figure of 17 Minority race MPs, it would require, by 1988 GRC 3MP-GRC standards, only 17 * 3 = 51 seats being allocated to GRCs out of a total of 87 seats contested (i.e. 87 - 51 = 36 SMCs)

Given to the fact that in the 2011 elections, 75 seats were sanctioned as GRC seats out of only 51 necessary (51 being generous as I show below), it can thus be said that of all parliamentary seats being categorized as GRC seats, only 51 / 75 = 68% were indeed necessary for the election of minorities into parliament. The other 32%, well, I guess the is the comfortable excess that the incumbent political party chooses to enjoy given to the fact that besides dissuading independents from contesting in general elections, smaller political parties would also be excessively disadvantaged due to their inability to form large teams (approx 5 men teams) to contest for bloated GRC positions.
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A more extreme calculation would consider the following considerations/ assumptions:
Given to the fact that several minority race candidates representing both PAP and the opposition had successfully won elections prior to the implementation of the GRC system of elections “Singapore’s history has shown that, in the past, minority candidates stood and won single seats. PAP MPs such as Mr Dhanabalan, Mr Rajaratnam, Mr Sidek Saniff and Mr Zulkifli Mohd have done so; so have opposition leaders like Mr Jeyaretnam in Anson, a predominantly Chinese constituency. This was so even in the 1984 GE.” ['sgpolitics', 28Aug2008] Sylvia Lim opposed motion to revise Parliamentary Elections Act because the motion sought to entrench GRCs | Sgpolitics.net , it could be safely assumed that minority candidates would perform better without the imposing, and much abused GRC system of elections besides providing a false sense of representation of minorities that their views are represented in Parliament, avoid the obscene distortions in of 75/87= 86.21% of all parliamentary seats being reserved explicitly for the purposes of minority representation (a gross and unnecessary distortion that only rouses animosity between races), perhaps with a minimum 33.3% minority MP per GRC rule where in the context of GRCs being on average 5 MPs each, two of the five shall be of a minority race. (Aljunied, Ang Mo Kio, Bishan-Toa Payoh, Holland-Bukit Timah, Jurong, Nee Soon, Pasir Ris-Punggol, Sembawang GRCs all fulfill this criteria of 2 minority MPs; with Holland-Bukit Timah standing out by having 2 of 4 MPs being of a minority race)

In fact, given to the availability of the NCMP system to allow for the admission of 'best performing losers' to be admitted to parliament; a legislation could also be passed so that besides having say 66.6% of non-Chinese races being represented in parliament as MPs, the extra 33.3%, if not duly elected would have the opportunity to sit in as minority race NCMPs! That said, I am hopeful that this wouldn't be necessary because with fewer distortions caused by the GRC system of elections, minority candidates wouldn't be judged as 'racially challenged' individuals requiring an 86.21% distortion of parliamentary elections to mandate their representation, but as decent and notable individual in their own light, capable and competent of representing their electorate; a job in which only the human touch should be necessary.

Thus using a 66.6% mandated minority representation rate in the context of today's 87 seat parliament and a non-Chinese population of 25.9%, the number of mandated minority candidates is = 66.6% * 25.9% * 87 = 15.006978 minority MPs.

Using 15 as the number of minority MPs necessary in an average distribution of 2 minority MPs per 5 member team GRC in the general configuration of: 7 * 5 member GRCs (with 2 minority MPs each) as well as 1 * 3 member GRC (with 1 minority MP in it), the total seats allocated for GRC MPs in support to the mandatory minority MP scheme shall be= (7 * 5) + (1 * 3) = 38 MP seats out of a 87 MP seat parliament.
Given the current PAP suited behemoth GRC configurations occupying 75 seats rather than the 38 calculated as necessary, it can be said that in the 2011 elections, the number of GRC MP seats was unnecessarily inflated by 37 seats.

As a fraction of the total number of seats utilized under the 2011 GRC MP scheme, the % of seats truly relevant to minority representation would be 38/75= 50.666%. I.e., 100% - 50.666 = 49.333% of MP seats mandated by the incumbent government are irrelevant to the representation of minority race in parliament but rather an opportunistic exploitation of citizen ignorance by the incumbent government to minimize the political competition by smaller political parties and independents in Singapore general elections by forcing them into a lose-lose situation of competing against the PAP for extremely limited SMC seats.

In conclusion, between 32 to 49.333% of parliamentary seats reserved by the GRC system for minority representation are irrelevant/ unnecessary for its mandated cause but rather an exploitative and opportunistic policy manipulation of the system for the purpose of insidious partisan political gain.

References:
- Singapore 2011: List of constituencies [Parl of SG]: List of Constituencies | Parliament Of Singapore
- Demographics of Singapore [wiki]: Demographics of Singapore - Wikipedia, the free encyclopedia
- [Table1]: Yeo Lay Hwee. “Electoral Politics in Singapore”*Electoral Politics in Southeast And East Asia, eds. Aurel Croissant, Gabriele Bruns & Marei John (Singapore: Friedrich Ebert Stiftung - Office for Regional Cooperation, 2002). http://library.fes.de/pdf-files/iez/01361007.pdf