Relation between current voltage .Acc. to ohm's law and P=IV
Note first of all that the resistance of an incandescent light bulb is not constant. The resistance of the filament increases significantly as the filament temperature increases, so the resistance of a cold bulb is much less than the resistance of a hot bulb.

Now the first question specifies that the voltage will only change marginally, which is a way of saying that the temperature of the bulb won't change much. So, for this question and in these specific circumstances, we assume that the resistance of the bulb does not change. Therefore, Ohm's Law (\$V = R \times I\$) says that current through the bulb and voltage across the bulb will be proportional...as one goes up the other must go up.

The second question involves Watt's Law, \$P = V \times I\$. The power consumed by an element is equal to the current through the element times the voltage across the element. If we assume that the amount of power consumed is constant, as this question does, then we now see that as the voltage goes up the current must go down.

The difference between the two cases is that one assumes constant resistance and the other assumes constant power.