How many different PPI does the model with ppcm of 87 have?
create table table_27653752_1 (ppi__pixels_per_inch__ varchar, ppcm__pixels_per_cm__ varchar, PRIMARY KEY (ppi__pixels_per_inch__))
select count(ppi__pixels_per_inch__) from table_27653752_1 where ppcm__pixels_per_cm__ = 87