Question

If a sack of dried dog food feeds 4 dogs or 5 puppies for one week, then 5 sacks of food will feed 15 puppies, and how many dogs?
A. 6
B. 7
C. 8
D. 9

Answer 1

Hint: It is given that one sack can feed 4 dogs or 5 puppies for a week. Then let’s suppose that 5 sacks of food will feed 15 puppies and $x$ dogs. Now by unitary method, as one sack is feeding 5 puppies so, 3 sacks will feed 15 puppies. Now the remaining 2 sacks will be used by dogs, so calculate the value of $x$ by the relation 4 dogs can feed on 1 sack for a week.

Complete step-by-step solution:
It is given in the question that a sack of dried dog food feeds 4 dogs or 5 puppies. There are two statements hidden in it, which are
1. One sack of food can feed 4 dogs
2. One sack of food can feed 5 puppies
Now, it is given that we have a total of 5 sacks of food.
Let us suppose that we can feed $x$ dogs and 15 puppies for one week using those 5 sacks of food.
We know that 5 puppies can feed on 1 sack of food.
Then 1 puppy can feed on $\dfrac{1}{5}$ sack of food.
Similarly, 15 puppies can feed on $\dfrac{1}{5}\times 15=3$ sacks of food.
As 15 puppies will require 3 sacks of food so now we have the remaining 2 sacks out of 5 to feed dogs.
We know that 1 sack of food can feed 4 dogs.
Then 2 sack of food can feed $4\times 2=8$ dogs.
Here, the value of $x=8$.
Hence, 5 sacks of food can feed 15 puppies and 8 dogs for one week.
So, Option (C) is the correct answer.

Note: This is a simple question of the unitary method. However, one trickier part in the question is to formulate an equation with the first statement which is a sack of dried dog food feeds 4 dogs or 5 puppies for one week. Students often get confused with this statement and interpret that both dogs and puppies combined are feeding on one sack for one week which is wrong. In that statement “or” indicates that either puppies or dogs are feeding on that one sack for a week. Using this interpretation formulate equations and get the correct answer.