Notice that the two digits of each answer always add up to make 9, and that each first digit of the answer is just one less than the multiple. For example, 9×5=45, the answer will begin with one less than the multiple 5, and the two digits of the answer must add to make 9, therefore it can be nothing but 4 and 5, or 45. This is true in all cases except 9×11 an already known answer, but also only 9's in this answer. This simple idea, when once understood, will master the table of 9's.
Be sure that the children realize that 7×4 in the tables of 7's are the same in value as 4×7, so that the answer to 7×4 becomes familiar with learning the table of 4's. Ask the question both ways 7×4 and 4×7.
The Tables of Weights and Measures
Some of these we learn easily and always retain; some always seem confusing. These can be mastered by the use of the Number Code and the Visual picture combined. Some examples follow:
24 sheets = 1 quire, and 20 quires = one ream. The picture of Two Dozen Squires in a Nice Room, will fix these figures and terms in mind. Two Dozen is 24, Squires is a reminder for Quires. Nice is 20 (2 is N and 0 is C) and room a reminder for Ream.
16-1/2 Feet = 1 Rod, 320 Rods = 1 Mile. Picture a Dish and a Half balanced on a Rod. Dish is your code word for 16 (1 is D and 6 is sh) and the Half Dish makes 16-1/2 Feet on (in) a Rod. Next—Many's the Rod in a Mile. Many's is 320 or the number of rods in a mile.
30-1/4 Sq. Yards = 1 Sq. Rod. Picture—MISTER takes a yard stick and measures off a Sq. Rod. Mister is 3-0-1-4, or 30-1/4.
160 Sq. Rods = 1 Acre. Picture—See a pile of Dishes out in the Acre being broken up by a rod. Dishes is 160 the number of Sq. Rods in an Acre.
640 Acres in a Sq. Mile. Picture—Take the Shears and cut up the mile into squares. Shears is 640, the number of Acres in a Sq. Mile.
792 Inches—1 Link. Picture—792 is Cabin, see the link hanging on the side of the cabin.