Question 252232
c = cost per kilowatt hour
k = number of kilowatt hours.


you get:


c*k = 50


that was last february.


this february the bill is:


.92*c*1.2*k = ?????


this is the same as:


.92*1.2*c*k = ?????


we know that c*k is equal to $50.00, so the equation becomes:


.92*1.2*50 = ?????


this becomes:


.92*1.2*50 = 55.2


this years bill should be $55.20


55.2/50 = 1.104 - 1 = .104 * 100% = 10.4%.


rounded to the nearest integer, this because a 10% increase which would be selection B.


example:


assume the cost per kilowatt hour was 20 cents / 100 = $.20


if the bill was 50, then the kilowatt hours were 250.


drop the cost by 8% to get c = .2 * (1-.08) = .2 * .92 = .184 per kilowatt hour.


raise the number of kilowatt hours by 20% to get 250 * (1 + .2) = 250 * 1.2 = 300 kilowatt hours.


figures for last february were:


c = .2
k = 250


figures for this february are:


c = .184
k = 300


.184 * 300 = 55.2


cost for last february was $50.00
cost for this february is $55.20


55.2 / 50 = 1.104 - 1 = .104 * 100% = 10.4% rounded to the nearest integer = 10%.