Solution:
Concept:
To solve this question, we will use the divisibility rule for 18
Divisibility of 18 – A number is divisible by 18 if the number is divisible by both 2 and 9.
From the question,
Divisibility of 9 – A number is divisible by 9 if the sum of all the digits is divisible by 9.
The total before tax given is
Step 1:
From the question, we can see that the total amount is divisible by 2 because the amount ends with an even number 6
Step 2:
Figure out the number so that it can be divisible by 9
Divisibility of 9 – A number is divisible by 9 if the sum of all the digits is divisible by 9.
The total before tax given is
Let the unknown number be
The sum of the number will be
By try and error method
The only number divisible by 9 from 20 to 30 is
Hence,
Therefore,
The unknown digit is = 7
Each cookie will cost
Hence,
Each cookie will cost = $4.32