Question 9 - Mind the Mistake, Mend the Mistake - Chapter 7 Class 7 - Finding the Unknown (Ganita Prakash II)

Transcript

Question 9 The following are some equations along with the steps used to solve them to find the value of the letter−number. Go through each solution and decide whether the steps are correct. If there is a mistake, describe the mistake, correct it and solve the equation.Is there a mistake? Yes What went wrong? The student divided the right side by 3, but only applied it to the 9, ignoring the 5y. If you divide one side by 3, you must divide the entire other side by 3. Correct solution Now, 3(7y + 4) = 9 + 5y Opening bracket 3 × 7y + 3 × 4 = 9 + 5y 21y + 12 = 9 + 5y Taking 12 on right side, it becomes subtraction 21y = 9 + 5y – 12 21y = 5y + 9 – 12 21y = 5y – 12 + 9 21y = 5y – (12 – 9) 21y = 5y – 3 Taking 5y on left side, it becomes subtraction 21y – 5y = –3 16y = –3 Taking 16 on right side, it becomes division y = (−𝟑)/𝟏𝟔