Example 9 - Chapter 7 Class 7 - Finding the Unknown (Ganita Prakash II)

Transcript

Example 9 Two friends want to save money. Jahnavi starts with an initial amount of ₹4000, and in addition, saves ₹650 per month. Sunita starts with ₹5050 and saves ₹500 per month. After how many months will they have the same amount of money?We have two people starting with different amounts and saving at different speeds. We want to know when they will be equal. Let m = Number of months Now, we find amount saved in m months by Jahnavi and Sunta Jahanvi Jahnavi starts with an initial amount of ₹4000, and in addition, saves ₹650 per month Thus, Amount saved = 4000 + 650 × Number of months = 4000 + 650 × m = 4000 + 650m Sunita Sunita starts with ₹5050 and saves ₹500 per month Thus, Amount saved = 5050 + 500 × Number of months = 5050 + 500 × m = 5050 + 500m Since both Amounts are equal after m months We write 4000 + 650m = 5050 + 500m Taking 500m left side (we don’t take 650m left side as 500m – 650m will be negative) 4000 + 650m – 500m = 5050 Taking 4000 left side 650m – 500 m = 5050 – 4000 150m = 1050 m = 1050/150 m = 7 Thus, After 7 months, both friends will have the exact same amount of money.