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Number Sense Book Part 1 Dts

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Number Sense Lessons

Number Sense Lessons

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  • 1. Number Sense Number Sense is memorization and practice. The secret to getting good at number sense is to learn how to recognize and then do the rules accurately . Then learn how to do them quickly. Every practice should be under a time limit.
  • 2. The First Step
    • The first step in learning number sense should be to memorize
    • PERFECT SQUARES from 1 2 = 1 to 402 = 1600
    • PERFECT CUBES from 1 3 = 1 to 253 = 15625
    • These squares and cubes should be learned in both directions. ie. 17 2 = 289 and the
  • 3. 2 x 2 Foil (LIOF) Working Backwards
    • The last number is the units digit of the product of the unit’s digits
    • Multiply the outside, multiply the inside
    • Add the outside and the inside together plus any carry and write down the units digit
    • Multiply the first digits together and add and carry.
    • Write down the number
  • 4. Squaring Numbers Ending In 5
    • First two digits = the ten’s digit times one more than the ten’s digit.
    • Last two digits are always 25
  • 5. Ending In 5 Consecutive Decades
    • First two digits = the small ten’s digit times one more than the large ten’s digit.
    • Last two digits are always 75
  • 6. Ending In 5 Ten’s Digits Both Even
    • First two digits = the product of the ten’s digits plus ½ the sum of the ten’s digits.
    • Last two digits are always 25
  • 7. Ten’s Digits Both Odd – Ending In 5
    • First two digits = the product of the ten’s digits plus ½ the sum of the ten’s digits.
    • Last two digits are always 25
  • 8. Ending in 5 Ten’s Digits Odd & Even
    • First two digits = the product of the ten’s digits plus ½ the sum of the ten’s digits. Always drop the remainder.
    • Last two digits are always 75
  • 9. Multiplying By 12 ½ (1/8 Rule)
    • Divide the non-12 ½ number by 8.
    • Add two zeroes.
  • 10. Multiplying By 16 2/3 (1/6 Rule)
    • Divide the non-16 2/3 number by 6.
    • Add two zeroes.
  • 11. Multiplying By 33 1/3 (1/3 Rule)
    • Divide the non-33 1/3 number by 3.
    • Add two zeroes.
  • 12. Multiplying By 25 (1/4 Rule)
    • Divide the non-25 number by 4.
    • Add two zeroes.
  • 13. Multiplying By 50 (1/2 Rule)
    • Divide the non-50 number by 2.
    • Add two zeroes.
  • 14. Multiplying By 75 3/4 Rule
    • Divide the non-75 number by 4.
    • Multiply by 3.
    • Add two zeroes.
  • 15. Multiplying By 125 1/8 Rule
    • Divide the non-125 number by 8.
    • Add three zeroes.
  • 16. Multiplying When Tens Digits Are Equal & The Unit Digits Add To 10
    • First two digits are the tens digit times one more than the tens digit
    • Last two digits are the product of the units digits.
  • 17. Multiplying When Tens Digits Add To 10 & The Units Digits Are Equal
    • First two digits are the product of the tens digit plus the units digit
    • Last two digits are the product of the units digits.
  • 18. Multiplying Two Numbers in the 90’s
    • Find out how far each number is from 100
    • The 1 st two numbers equal the sum of the differences subtracted from 100
    • The last two numbers equal the product of the differences
  • 19. Multiplying Two Numbers Near 100
    • First Number is always 1
    • The middle two numbers = the sum on the units digits
    • The last two digits = the product of the units digits
  • 20. Multiplying Two Numbers With First Numbers Equal & A Zero In The Middle
    • The 1 st two numbers = the product of the hundreds digits
    • The middle two numbers = the sum of the units x the hundreds digit
    • The last two digits = the product of the units digits
  • 21. Multiplying By 3367 (10101 Rule)
    • Divide the non-3367 number by 3
    • Multiply by 10101
  • 22. Multiplying A 2-Digit Number By 11 (121 Pattern)
    • Last digit is the units digit
    • The middle digit is the sum of the tens and the units digits
    • The first digit is the tens digit + any carry
    Work Right to Left Work Right to Left Work Right to Left Work Right to Left Work Right to Left
  • 23. Multiplying A 3-Digit Number By 111 (1221 Pattern)
    • Last digit is the units digit
    • The next digit is the sum of the tens and the units digits
    • The next digit is the sum of the tens and the hundreds digit + carry
    • The first digit is the hundreds digit + any carry
    Work Right to Left Work Right to Left Work Right to Left Work Right to Left Work Right to Left
  • 24. Multiplying A 3-Digit Number By 111 (12321 Pattern)
    • Always work from Right to Left Last digit is the units digit
    • The next digit is the sum of the tens and the units digits
    • The next digit is the sum of the units, tens and hundreds digits + carry
    • The next digit is the sum of the tens and hundreds digits + carry
    • The next digit is the hundreds digit + carry
    Work Right to Left Work Right to Left Work Right to Left Work Right to Left Work Right to Left
  • 25. Multiplying A 3-Digit Number By 111 (12321 Pattern) Work Right to Left Work Right to Left Work Right to Left Work Right to Left Work Right to Left
  • 26.  

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