Answer:
Jackie cut the cake into ten equal pieces, so each piece is 1/10 of the original cake.
If she had four-tenths of the cake left after dinner, then she had 6/10 of the cake left.
She wrapped a piece that was one-fifth of the original cake for her sister. One-fifth of the original cake is 1/5 x 1 = 1/5.
So, Jackie gave away 1/5 of the cake and had 6/10 - 1/5 = 3/10 of the cake left.
Therefore, the fraction of the cake that was left is 3/10.