A sickle-cell carrier man marries a woman who is carrier for...

Sickle-cell anaemia is an autosomal recessive disorder.

Let the normal allele be $Hb^A$ and the sickle-cell allele be $Hb^S$.

The genotype of the carrier man is $Hb^A Hb^S$ and the carrier woman is $Hb^A Hb^S$.

The cross between them is $Hb^A Hb^S \times Hb^A Hb^S$.

The possible genotypes of the offspring are:
$25\%Hb^A Hb^A$ (Normal)
$50\%Hb^A Hb^S$ (Carrier)
$25\%Hb^S Hb^S$ (Affected)

The chances of having carrier children is $50\%$.

Answer: $50\%$ of them will be carriers.