Example 11 - Chapter 7 Class 7 - Finding the Unknown (Ganita Prakash II)

Transcript

Example 11 Riyaz created a math trick, which he tries out on his friend Akash. Riyaz asked Akash to perform the following steps without revealing the answer to any of the intermediate steps. 1. Think of a number. 2. Subtract 3 from the number. 3. Multiply the result by 4. 4. Add 8 to the product. 5. Reveal the final answer. The final answer revealed by Akash was 24. Using this, Riyaz correctly figured out the starting number that Akash had thought of. Find this number. We do the steps one-by-one Let’s assume our Number is x Steps Expression Think of a number. Subtract 3 from the number. Multiply the result by 4.Add 8 to the product. 4 × (x – 3) + 8 4 × (x – 3) And, the final answer is 24 So, our equation becomes 4 × (x – 3) + 8 = 24 Solving 4(x – 3) + 8 = 24 Opening bracket 4x – 4 × 3 + 8 = 24 4x – 12 + 8 = 24 4x – (12 – 8) = 24 4x – 4 = 24 Taking –4 to right side, it becomes + 4 4x =24 + 4 4x = 28 Taking 4 to right side, it becomes division x = 28/4 x = 7 Thus, Akash thought of the number 7