Theory:

To verify a bill, we should ask a few probing questions to ourselves.
 
Probing questions:
Probing questions help us analyze a problem to have an in-depth knowledge about the same. They are generally open-ended questions. Probing questions can only be answered with a yes or a no.
Example:
1. Have I bought all three items?

2. Have I paid the right amount?
 
3. Have I got the right amount back?
Let us consider the bill given below and try to come up with a few probing questions.
 
XYZ Stationery Store, Tamil Nadu
 
Bill Number: \(120\)
 
Date: \(1-12-2020\)
 
S. No.
Items
Quantity
(in nos.)
Rate
(per item)
Amount
(in \(Rs.\))
1
Notebook
\(3\)
\(10\)
\(30\)
2
Pen
\(2\)
\(5\)
\(10\)
3
Pencil
\(4\)
\(2\)
\(8\)
4
Ruler
\(1\)
\(7\)
\(7\)
 
Total amount to be paid: \(Rs.55\)
 
 
1. Do I have the right bill?
 
Yes.
 
I have the bill dated \(1-12-2020\), and also the bill number is \(120\).
 
 
2. Have I paid the right amount for the notebooks?
 
Yes.
 
Number of notebooks \(= 3\)
 
Rate of one notebook \(= Rs.10\)
 
The amount to be paid for the notebooks \(= 3\) \(×\) \(10 = Rs.30\)
 
 
3. Have I paid the right amount for the pens?

Yes.

Number of pens \(= 2\)

Rate of one pen \(= Rs.5\)

The amount to be paid for the pens \(= 2\) \(×\) \(5 = Rs.10\)
 
 
4. Have I paid the right amount for the pencils?

Yes
.

Number of pencils \(= 4\)

Rate of one pencil \(= Rs.2\)
The amount to be paid for the books \(= 4\) \(×\) \(2 = Rs.8\)
 
 
5. Have I paid the right amount for the rulers?

Yes.

Number of ruler(s) \(= 1\)

Rate of one ruler \(= Rs.7\)
The amount to be paid for the ruler: \(1\) \(×\) \(7 = Rs.7\)
 
 
6. Is the total amount to be paid correct?
  
Yes.
 
The total amount to be paid is the addition of the amounts to be paid for each of the items.
 
Total amount to be paid \(= 30 + 10 + 8 + 7 = Rs.55\)
 
 
7. Have I bought \(5\) items?
 
No.
 
According to the bill, I have bought \(9\) items. The items are \(3\) notebooks, \(2\) pens, \(4\) pencils and \(1\) ruler.
 
\(3 + 2 + 4 + 1 = 10\)