4 - 1 4 ÷ 1 4 - 2 4 ÷ 2 11 (or 21 or 31, etc.) + 1 4 - 3 1 × 2 4 ÷ 3 11 " + 2 4 - 4 2 × 2 4 ÷ 4 11 " + 3 3 × 2 11 " + 4 4 × 2 11 " + 5 5 - 1 5 × 2 5 ÷ 1 11 " + 6 5 - 2 6 × 2 5 ÷ 2 11 " + 7 5 - 3 7 × 2 5 ÷ 3 11 " + 8 5 - 4 8 × 2 5 ÷ 4 11 " + 9 5 - 5 9 × 2 5 ÷ 5 6 - 1 1 × 3 6 ÷ 1 2 + 1 6 - 2 2 × 3 6 ÷ 2 2 + 2 6 - 3 3 × 3 6 ÷ 3 2 + 3 6 - 4 4 × 3 6 ÷ 4 2 + 4 6 - 5 5 × 3 6 ÷ 5 2 + 5 6 - 6 6 × 3 6 ÷ 6 2 + 6 7 × 3 2 + 7 8 × 3 2 + 8 7 - 1 9 × 3 7 ÷ 1 2 + 9 7 - 2 7 ÷ 2 7 - 3 7 ÷ 3 7 - 4 1 × 4 7 ÷ 4 12 (or 22 or 32, etc.) + 1 7 - 5 2 × 4 7 ÷ 5 12 " + 2 7 - 6 and so on 7 ÷ 6 7 - 7 to 9 × 9 7 ÷ 7 and so on to and so on and so on to 9 + 9 to 18 - 9 82 ÷ 9 19 (or 29 or 39, etc.) + 9 83 ÷ 9, etc. If estimating for the entire series is too long a task, it will be sufficient to use eight or ten from each, say:-- 3 + 2 13, 23, etc. + 2 7 + 2 17, 27, etc. + 2 " 3 " 3 " 3 " 3 " 4 " 4 " 4 " 4 " 5 " 5 " 5 " 5 " 6 " 6 " 6 " 6 " 7 " 7 " 7 " 7 " 8 " 8 " 8 " 8 " 9 " 9 " 9 " 9 3 - 3 7 - 7 9 × 7 63 ÷ 9 4 " 8 " 7 × 9 64 " 5 " 9 " 8 × 6 65 " 6 " 10 " 6 × 8 66 " 7 " 11 " 67 " 8 " 12 " 68 " 9 " 13 " 69 " 10 " 14 " 70 " 11 " 15 " 71 " 12 " 16 " TABLE 2 ESTIMATES OF THE AMOUNT OF PRACTICE PROVIDED IN BOOKS I AND II OF THE AVERAGE THREE-BOOK TEXT IN ARITHMETIC; BY 50 EXPERIENCED TEACHERS