The following table shows the number of hours some students in two neighborhoods

Someone posted a explanation to help everyone so i would copy and paste it for you. “Whenever you have an increase, you multiply by (100% + increase%) and whenever you have a decrease you multiply by (100% - decrease%). So for each pair, let's do that. A 30% increase followed by a 15% decrease. = ? (1 + 0.3)*(1 - 0.15) = 1.3*0.85 = 1.105. Result is greater than original. A 70% increase followed by a 50% decrease. = ? (1 + 0.7)*(1 - 0.5) = 1.7 * 0.5 = 0.85. Result is less than original. A $35 decrease followed by a $25 increase = ? Tricky. No percentages. So -35 + 25 = -10. So value is less than original. A 50% increase followed by a 33/1/3% decrease. = ? (1 + 0.5)*(1 - 0.3333333) = 1.5 * 0.666667 = 1. Result is same as original. A 50% decrease followed by a 100% increase. = ? (1 - 0.5)*(1 + 1) = 0.5 * 2 = 1. Result is same as original.”