NCERT Class 6 Solutions: Whole Numbers (Chapter 2) Exercise 2.2–Part 1

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Q-1 Find the sum by suitable rearrangement:

  1. Equation

  2. Equation

Solution:

The idea is to pair the numbers so that their least significant (right-most) digits add to either 5 or better still to 10. For example when asked to add 11 + 12 + 19. First do 11 + 19 = 30 (notice how the total has 0 in right-most digit). Now it is easy to 30 + 12 = 42.

  1. Equation

    • Rearrange the sum, Equation

      Equation

      Equation

  2. Equation

  • Equation

    Equation

    Equation

Q-2 Find the product by suitable arrangement

  1. Equation

  2. Equation

  3. Equation

  4. Equation

  5. Equation

  6. Equation

Solution:

The idea is to pair the numbers so that a number ending in 5 is multiplied with an even number. This would produce 0 in the least significant. For example when asked to calculate Equation . First do Equation = 180 (notice how the total has 0 in right-most digit). Now it is easy to do Equation = 1260 (we could ignore the zero, then multiply and then add back the zero).

It is easy to multiply even number with 5

Multilication by 5

It is easy to multiply even number with 5

  1. Equation

    Equation

    Equation

    Equation

  2. Equation

    Equation

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    Equation

    Note here we choose to multiply 4 with 25 (even though 166 was also even), this was because we got 100 makes it very easy to multiply further.

  3. Equation

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    Here 8 is even.

  4. Equation

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    Here 16 is even.

  5. Equation

    Equation

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    Here 60 is the even number.

  6. Equation

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    We know that product of 8 and 125 is 1000 and so we make a pair out of them. We also know that 4 multiplied with 25 would be 100 so product of 40 and 25 would also be 1000.

Q-3 Find the value of the following:

  1. Equation

  2. Equation

  3. Equation

  4. Equation

Solution:

You can distribute multiplication over addition and subtraction:

Describing the distributive property

Image Describing the Distributive Property

Describing the distributive property

Multiplication is distributibe over addition.

Distributing Property of Multiplication Over Addition

Multiplication is distributibe over addition.

Multiplication is distributibe over subtration.

Distributing Property of Multiplication Over Subtraction

Multiplication is distributibe over subtration.

  1. Equation

    Equation

    Equation

    Equation

  2. Equation

    Equation

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    Equation

  3. Equation

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    Equation

  4. Equation

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    Equation

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