SOLUTION: The electrician was upset. She knew that "b" batteries would power "d" circuits for 11 days, but she had "d" +8 circuits to power. How many days would "r" batteries last? Pleas

From the given data, the rate of consumption is    batteries per one circuit per day,  in the first case.


In the other case, the rate of consumption is  .


Assuming the the rate of consumption is the same in both cases, we can write this equation


     = .


In this proportion, the variable "r" is unknown.


Cancel "b" in both sides and express  "r"  from the proportion  r = .    ANSWER


Now, when the formula is obtained, you can easily interpret it by many different ways . . .