Class 7 Maths Chapter 12 Exercise 12.2 Pdf Notes NCERT Solutions

Class 7 Maths Chapter 6 Algebraic Expression Exercise 12.2 pdf notes:-

Exercise 12.2 Class 7 maths Chapter 12 Pdf Notes:-

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ADDITION AND SUBTRACTION OF ALGEBRAIC
EXPRESSIONS

Consider the following problems:

  1. Sarita has some marbles. Ameena has 10 more. Appu says that he has 3 more
    marbles than the number of marbles Sarita and Ameena together have. How do you
    get the number of marbles that Appu has?
    Since it is not given how many marbles Sarita has, we shall take it to be x. Ameena
    then has 10 more, i.e., x + 10. Appu says that he has 3 more marbles than what
    Sarita and Ameena have together. So we take the sum of the numbers of Sarita’s

marbles and Ameena’s marbles, and to this sum add 3, that is, we take the sum of
x, x + 10 and 3.

  1. Ramu’s father’s present age is 3 times Ramu’s age. Ramu’s grandfather’s age is 13
    years more than the sum of Ramu’s age and Ramu’s father’s age. How do you find
    Ramu’s grandfather’s age?
    Since Ramu’s age is not given, let us take it to be y years. Then his father’s age is
    3y years. To find Ramu’s grandfather’s age we have to take the sum of Ramu’s age (y)
    and his father’s age (3y) and to the sum add 13, that is, we have to take the sum of
    y, 3y and 13.
  2. In a garden, roses and marigolds are planted in square plots. The length of the
    square plot in which marigolds are planted is 3 metres greater than the length of the
    square plot in which roses are planted. How much bigger in area is the marigold plot
    than the rose plot?
    Let us take l metres to be length of the side of the rose plot. The length of the side of
    the marigold plot will be (l + 3) metres. Their respective areas will be l
    2
    and (l + 3)2
    .
    The difference between (l2 + 3)2
    and l2
    will decide how much bigger in area the
    marigold plot is.
    In all the three situations, we had to carry out addition or subtraction of algebraic
    expressions. There are a number of real life problems in which we need to use
    expressions and do arithmetic operations on them. In this section, we shall see how
    algebraic expressions are added and subtracted.

Thus, the sum of two or more like terms is a like term with a numerical coefficient
equal to the sum of the numerical coefficients of all the like terms.
Similarly, the difference between two like terms is a like term with a numerical
coefficient equal to the difference between the numerical coefficients of the two
like terms.
Note, unlike terms cannot be added or subtracted the way like terms are added
or subtracted. We have already seen examples of this, when 5 is added to x, we write the
result as (x + 5). Observe that in (x + 5) both the terms 5 and x are retained.
Similarly, if we add the unlike terms 3xy and 7, the sum is 3xy + 7.
If we subtract 7 from 3xy, the result is 3xy – 7

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