Mental Arithmetic (Rules 1-5) Flashcards Preview

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Flashcards in Mental Arithmetic (Rules 1-5) Deck (95)
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1

What is Rule 1?

If the first digits are the same and the second digits are both 5s then you add 1 to the first digit in the first row and then multiply.

2

What is Rule 2?

If first digits are the same numbers and the second digits add up to ten then you add 1 to the first digit in the first row and then multiple

3

What is Rule 3?

If the first digits add up to ten and the second set of digits are the same then you multiply the last row and place the answer, then multiply the first digits and add one of the numbers in the second row of digits

4

What is rule 4?

Difference of Squares. a^2 - b^2 = (a-b) (a+b) If the difference between two numbers is equal then square the number that is directly between them MINUS how far they are apart^2 SO: (29)(31) = (30 -1)(30+1) 30^2 - 1^2 900 - 1 = 899

5

What is rule 5?

Any 2-digit number times 11 will equal the first digit in the 2 digit number, the second digit = first digit + second digit of the first two digit number, third digit equals the second digit in the 2 digit number. SO 43 x 11 = 4,(7 (4+3)),3

6

(45) (65)

2925

7

(55) (55)

3025

8

(14) (94)

1316

9

(24) (84)

2016

10

(34) (74)

2516

11

(44) (64)

2816

12

(13) (93)

1209

13

(23) (83)

1909

14

(33) (73)

2409

15

(43) (63)

2709

16

(12) (92)

1104

17

(22) (82)

1804

18

(32) (72)

2304

19

(42) (62)

2604

20

(11) (91)

1001

21

(21) (81)

1701

22

(31) (71)

2201

23

(41) (61)

2501

24

(51) (51)

2601

25

(52) (52)

2704

26

(53) (53)

2809

27

(54) (54)

2916

28

(55) (55)

3025

29

(56) (56)

3136

30

(57) (57)

3249