Commercial Mathematics • Topic 1 of 3

Bills, Invoices, and Banking Basics

What is a Bill or Invoice?

A bill (or invoice) is a document that lists items purchased, their prices, quantities, and the total amount due. It is issued by a seller to a buyer.

Components of a Bill:

  • Date of purchase
  • Item description and quantity
  • Rate (price per unit)
  • Amount (quantity × rate)
  • Subtotal (sum of all amounts)
  • Taxes (GST, sales tax, etc.)
  • Total amount (subtotal + taxes)

What is Banking?

Banking involves keeping money safe in a bank account, earning interest, and making payments. Common account types:

  • Savings Account: For daily transactions; earns low interest
  • Current Account: For businesses with many transactions; no interest
  • Fixed Deposit (FD): Lump sum for fixed period; higher interest

Key Banking Terms:

TermMeaning
Principal (P)Amount deposited or borrowed
InterestExtra money earned on deposits
Simple Interest (SI)\(I = \frac{P \times R \times T}{100}\)
Amount (A)Principal + Interest
Rate (R)Percentage of interest per year
Time (T)Duration in years
Bills, Invoices and BankingINVOICEItemQtyRateAmountNotebooks5₹45₹225Pens (box)2₹120₹240Ruler3₹25₹75Subtotal₹540GST (18%)₹97.20TOTAL₹637.20Banking TermsPrincipal:Money depositedInterest:Earnings on depositCheque:Written payment orderDebit:Money going outCredit:Money coming inBalance:Amount remaining
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Worked Example

Calculate the total amount of a bill with: 3 shirts at ₹450 each, 2 pants at ₹800 each, and GST 8%.

Solution
  • Shirts: \(3 \times 450 = ₹1350\)
  • Pants: \(2 \times 800 = ₹1600\)
  • Subtotal = \(1350 + 1600 = ₹2950\)
  • GST = \(8\% \text{ of } 2950 = \frac{8}{100} \times 2950 = ₹236\)
  • Total = \(2950 + 236 = ₹3186\)

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Answer: ₹3186 **Example 2:** Ravi deposits ₹5000 in a savings account at 5% simple interest per annum. Find the interest and amount after 2 years. *Solution:* - $P = 5000$, $R = 5\%$, $T = 2$ years - $I = \frac{P \times R \times T}{100} = \frac{5000 \times 5 \times 2}{100} = \frac{50000}{100} = ₹500$ - $A = P + I = 5000 + 500 = ₹5500$ - **Answer:** Interest = ₹500, Amount = ₹5500 **Example 3:** A bill has subtotal ₹2400 and total ₹2616. Find the GST percentage. *Solution:* - GST amount = Total - Subtotal = $2616 - 2400 = ₹216$ - GST percentage = $\frac{216}{2400} \times 100\% = \frac{21600}{2400} = 9\%$ - **Answer:** 9%

Key Points

  • A bill/invoice lists items, prices, taxes, and total amount
  • Banking involves deposits, withdrawals, and earning interest
  • Simple Interest formula: \(I = \frac{P \times R \times T}{100}\)
  • Amount = Principal + Interest
  • GST (Goods and Services Tax) is added to the subtotal
Tap an option to check your answer0 / 4
Q1.A bill lists the items bought and the:
Explanation: The total.
Q2.An invoice is a document requesting:
Explanation: Payment.
Q3.A deposit ___ money in a bank account.
Explanation: Adds.
Q4.The money remaining in an account is the:
Explanation: Balance.