Why is return value different ?

Hi, Experts

env

====

Sybase IQ 15.4

[query1]

select convert(numeric(18,1), 0.8488*100) from iq_dummy;

84.8

[query2]

select convert(numeric(18,1), 0.8488*100);

84.9

why are return values different ?

one is 84.8 the other is 84.9....??

thanks in advance...