Applying Percentage Increases and Decreases in Real-Life Financial Contexts for Grade 11

Editor's Notes

• #1 Welcome the class. Today's topic is Apply a percentage increase or decrease in various contexts:.
• #2 Welcome to Session 1 of Grade 11 General Mathematics. Today, we are moving beyond abstract numbers to understand how percentages dictate the world of finance, business, and your future paycheck. We will cover everything from why snacks get more expensive over time to how to read your very first salary slip.
• #3 Let's start with a trip down memory lane. Think back to when you were in Grade 1. How much was a small pack of biscuits or a bottle of juice? Now, look at the price today. Even if the product hasn't changed, the price has. This is the 'Purchasing Power' of your money. If your allowance stayed the same for 10 years, you'd be much hungrier today. Why does this happen? That's our first topic: Inflation.
• #4 Inflation is the decline of purchasing power. When we say inflation is 4%, it means that on average, things cost 4% more than they did last year. To calculate the impact, we treat it as a percentage increase. For example, if you had a 50-peso budget for jeepney fares, and inflation rose significantly, that 50 pesos can no longer take you the same distance it used to.
• #5 Let's test our initial understanding. Look at Question 1: If we add 4% to 100 pesos, what's the result? (Wait for student response). Correct, it's 104. Now, for Question 8 from your worksheet: Does inflation make your money more powerful or less? (Wait for response). Exactly, it decreases purchasing power. The answer is C.
• #6 Now let's step into the shoes of a business owner. You buy inventory at a 'Cost Price,' but you can't sell it at that price, or you'll go broke. You add a 'Mark-up.' But be careful! If you mark an item up by 20% and then give a 20% discount later, you actually end up with less than your original cost. Percentages are relative to the base they are applied to!
• #7 Let's do some quick math. For the shirt: 30% of 500 is 150. Add that to 500, and you get 650. For the jacket: 15% of 2,000 is 300 pesos off. And for the trader: The profit is 200 pesos. 200 divided by the cost of 800 is 0.25, or 25% profit. Always divide the profit by the original cost to get the percentage!
• #8 Every time you buy a burger or a gadget, you are paying VAT. If a receipt says the total is 1,120 pesos, you might think the tax is 120 pesos. Let's check: 1,000 times 1.12 is 1,120. So, the base price was 1,000. This is a crucial skill for businesses to calculate how much tax they need to remit to the government.
• #9 Using the logic we just discussed, the answer to question 3 is A: 1,000 pesos. Remember, don't just subtract 12% from the total; you must divide by 1.12 because the VAT was added to the original 100% price.
• #10 When you get your first job, you'll see two numbers: Gross and Net. Gross looks great, but Net is what actually enters your bank account. In the Philippines, we have mandatory contributions that help provide healthcare and retirement funds. Understanding how these percentages are deducted is vital for personal budgeting.
• #11 Let's solve the OT pay. 500 pesos for 8 hours is 62.50 per hour. 1.25 times 62.50 is 78.125 per OT hour. Multiply by 2 hours, and you get 156.25. The answer is B. Also, remember that SSS is a deduction (B), and Net Income is always Gross minus Deductions (B).
• #12 Math isn't just about numbers; it's about people. If the price of rice goes up by 10% but a worker's wage stays the same, that family has to eat less. As future business leaders, how will you set your mark-ups? As future citizens, how will you ensure your taxes are used properly? Mathematics gives you the tools to analyze these social issues fairly.
• #13 We've covered a lot today—from inflation to payroll. Your final task is to write a letter to your younger self. Explain one thing you learned today that you wish you knew earlier. Maybe it's about how VAT works, or why you should start saving early to beat inflation. Use the math we learned today to justify your advice. Class dismissed!