Answer
$0.4$
Work Step by Step
There are many possibilities for the first six chips: $6$ red chips, $5$ red chips and $1$ white chip, and so on. But, its is irrelevant if we don't know their colors (see example 2.4.8, page $42$)
$P(Seventh~chip~is~red)=P(First~chip~is~red)=\frac{40}{100}=0.4$
