The Junk Seller - Indian Currency

Indian Currency Units: The official currency of India is the Rupee ($₹$). Smaller amounts are measured in Paise ($p$). The conversion rule is $1 \text{ Rupee} = 100 \text{ Paise}$. Visually, imagine one $₹ 1$ coin being split into two 50-paise coins or four 25-paise coins to understand the value ratio.

Unitary Method for Total Cost: To find the total cost of several items, multiply the price of one item (the rate) by the total number of items or the weight. Visually, this is like looking at a 'Rate List' board at a junk shop where 1 kg of newspaper costs $₹ 5$, so 2 kg costs $₹ 10$.

Cost Price (CP) and Selling Price (SP): The 'Cost Price' is the money a seller pays to buy junk, and the 'Selling Price' is the money they receive when they sell it to a bigger shop. In a notebook ledger, CP is recorded as an expense (money going out) and SP is recorded as income (money coming in).

Profit and Loss: If the Selling Price is higher than the Cost Price ($SP > CP$), the seller makes a Profit. If the Cost Price is higher ($CP > SP$), the seller suffers a Loss. Visually, imagine a balance scale: if the 'Money Received' side is heavier than the 'Money Spent' side, you have earned a profit.

Loan and Interest: A loan is money borrowed from a bank or a person like a moneylender. Interest is the 'extra' money paid back along with the borrowed amount. For example, if you borrow $₹ 100$ and pay back $₹ 110$ after a month, the $₹ 10$ is the interest.

Mental Math Multiplication: To calculate costs quickly, use multiplication shortcuts for tens and hundreds. For instance, to calculate $6 \times 40$, first multiply $6 \times 4 = 24$ and then add a zero at the end to get $240$. This helps in calculating junk prices without using paper and pencil.

Splitting Numbers for Multiplication: Large numbers can be broken down to make multiplication easier. For example, $32 \times 8$ can be calculated visually as $(30 \times 8) + (2 \times 8)$, which is $240 + 16 = 256$.