Two shopkeepers sell the same article at the same price for the same quantity. One gives $25\%$ discount; the other offers $25\%$ more quantity at the same price. From a customer's view, which is better?
"More quantity at same price" $\Rightarrow$ divide price by the quantity factor to get the effective price per unit.
cannot be determined
Deal 1: price becomes $75\%$ of original (effective price factor $0.75$).
Deal 2: quantity becomes $125\%$; effective price per unit $=\frac{1}{1.25}=0.80$ of original.
Since $0.75 < 0.80$, Deal 1 is better.
An electricity utility company charges ₹7 per kWh. If a 40-watt desk light is left on for 10 hours each night for 180 days, what would be the cost of energy consumption? If the desk light is on for 2 more hours each night for the 180 days, what would be the percentage-increase in the cost of energy consumption?