Let's start by finding the new value of the stock in Company A after the decrease of 16%.
The new value of the stock in Company A is:
0.84 x $1800 = $1512
Similarly, the new value of the stock in Company B after the decrease of 20% is:
0.8 x $1930 = $1544
The total value of the investor's stock account now is:
$1512 + $1544 = $3056
To find the percentage decrease in the investor's stock account, we need to compare the total value of the account now to the total value of the account last year:
($1800 + $1930) = $3730
The percentage decrease is:
[(3730 - 3056)/3730] x 100% ≈ 18.1%
Therefore, the total percentage decrease in the investor's stock account is approximately 18.1%.