Fast Arithmetic Tips : Addition

1. Addition of 5 When adding 5 to a digit greater than 5, it is easier to first subtract 5 and then add 10. For example, 8 + 5 = 13. Also 8 - 5 = 3; 3 + 10 = 13. 12 + 5 = 17. Also 12 - 5 = 7; 7 + 10 = 17. 2. Subtraction of 5 When subtracting 5 from a number ending with a a digit smaller than 5, it is easier to first add 5 and then subtract 10. For example, 26 - 5 = 21. Also 26 + 5 = 31; 31 - 10 = 18. 23 - 5 = 18. Also 23 + 5 = 28; 28 - 10 = 18. 23 - 5 = 18. Also 23 + 5 = 28; 28 - 10 = 18. Division by 5 Similarly, it's often more convenient instead to multiply first by 2 and then divide by 10. For example, 1375/5 = 2750/10 = 275. 980/5 = 1960/10 = 196. Multiplication by 5 It's often more convenient instead of multiplying by 5 to multiply first by 10 and then divide by 2. For example, 140×5...

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