Answer:
Reduced by $4000
Step-by-step explanation:
Your account will be reduced by $4000 this is how it will happen
You sell at $40 and again bought it back at $40
And at the end of the day, it was back to $42
You will lose value as it was $50 before and $42 at the end of the day
Difference = $50 - $42 = $8
loss = $8 x 500 = $4,000
NOTE: However number of shares remain same.