Suppose that a lithium-ion cell having total charge capacity Q=10Ah is discharged at a rate of 1A for 30min. What is the net change in the cell's state of charge (in percent)? Round to the nearest percent.
$$\Delta Q = I \Delta T$$ right? You're given
$$ I = 1A \\ \Delta T = 0.5 h \\ \Delta Q = I \Delta T = 0.5 Ah \\ Q_0 = 10 Ah $$
Thus $$Q_0 - \Delta Q = 9.5 Ah$$ You subtract because of implications of the word "discharge". Alternatively you could say that the current
I is negative.