Chapter-4 (Currency And Exchange Rate) Important Formulas

Currency and Exchange Rate: Important Formulas

Mathematics • Grade 10 • Currency and Exchange Rate

Quick memory: The bank buys low and sells high. Selling rate > Buying rate.

1. Which Rate to Use?

You want to…	Bank action	Rate used
Change foreign money into NPR	Bank buys	Buying rate
Change NPR into foreign money	Bank sells	Selling rate
Foreign A into foreign B	Buys A, sells B	Buying rate of A, selling rate of B

2. Conversion Formulas

• Foreign → NPRRs. = Foreign amount × Buying rate
• NPR → ForeignForeign amount = Rs. ÷ Selling rate
• Foreign A → Foreign BB = (A × Buying rate of A) ÷ Selling rate of B
• Bank's gain per unitSelling rate − Buying rate

Units: Japanese Yen is quoted per 10 and South Korean Won per 100. Divide the rate by 10 or 100 for 1 unit. India: IC 100 = Rs. 160, so IC 1 = Rs. 1.60.

3. Chain Rule

• Write the given relations as A = B, B = C, C = D … ending with the unknown x.
• Start each new line with the currency that ended the line before.
• Product of left side = Product of right side

Example: $500 = £390, £50 = Rs. 7,547, Rs. 10,308 = $x

500 × 50 × 10,308 = 390 × 7,547 × x ⇒ x = $87.55

4. Change in Value of Currency

• Inflation (rate rises R%)New rate = Old rate × (1 + R/100)
• Deflation (rate falls R%)New rate = Old rate × (1 − R/100)
• Steps: (1) Find foreign amount at old rate. (2) Find new rate. (3) Change back at new rate. (4) Compare with the starting Rs.

• Profit or Loss = Final Rs. − Initial Rs.
• Final > Initial ⇒ Profit. Final < Initial ⇒ Loss.

Example: Rs. 7,20,000 at 1 Baht = Rs. 3.60; NPR deflates 5%

Baht = 2,00,000; new rate = 3.60 × 0.95 = 3.42; Rs. = 6,84,000. Loss = Rs. 36,000

5. Business, Tax and Profit

• Cost price with tax = Price + Tax% of Price
• Add taxes one after another: custom tax first, then VAT (13%) on the new total.
• Selling price = Cost price × (1 + Profit%/100)
• Profit % = (Profit ÷ Cost price) × 100
• Cost price = Selling price × 100 ÷ (100 + Profit%)
• Break-even price = total cost (no profit, no loss).

Example: 900 shawls at Rs. 4,000, 5% export tax, 20% profit, €1 = Rs. 130

CP = 36,00,000 × 1.05 = 37,80,000. SP = 37,80,000 × 1.2 = 45,36,000. € = 45,36,000 ÷ 130 = €34,892.30

6. Quick Reference

Item	Value
Declared by	Nepal Rastra Bank
Nepal–India rate	IC 100 = NRs. 160 (fixed)
Currency of China	Yuan
Student going abroad uses	Selling rate
Foreigner/worker sending money home to Nepal	Buying rate
Round answers to	2 decimal places

Exam tips: (1) Write the rate you are using. (2) Check the unit (10 or 100). (3) State "Profit" or "Loss" in the final line. (4) Show every step in chain-rule questions.

Currency and Exchange Rate • Grade 10 Mathematics