Problem
16. After 9 weeks Mikayla has an average mark of 5 out of 10 in the weekly spelling tests. What is the minimum number of extra weeks now required to raise her average to 7 ? (A) 4 (B) 5 (C) 6 (D) 7 (E) 8
Solution
Step 1 ：Find the total marks Mikayla has currently: Total marks = average * number of weeks = 5 * 9
Step 2 ：Let x be the number of extra weeks required. Solve for x in the equation: \(\frac{5 * 9 + 10 * x}{9 + x} = 7\)
Step 3 ：\boxed{6}
