Well, stacking those two would not be 26% off technically - they are applied one at a time. Kinda like 10% off + 10% off = 19% off instead of 20. ($100 - 10% = $90, then - 10% again = $81)
In this case, take a $100 item:
$100 - 16% = $84. Then, $84 - 10% = $75.60
Thus, 24.4% off is correct...