Answer
$411.8$
Work Step by Step
After a 42% increase, we find that the number of items you have will be:
$N_1=N_0(1+r)=500(1+0.42)=710$
After a 42% decrease, we find that the number of items you have will be:
$N=N_1(1-r)=710(1-0.42)=411.8$