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Example 10: Form the algebraic expressions for the following mathematical statements:

(a) 7 added to the thrice of the product of x and y.
(b) Difference of the double of a and b added to the thrice of the product of a and b.
(c) The total cost of x notebooks at `35 each and the cost of y pencils at `8 each.

(d) Subtract the product of 4, b and c from the
square of a. In an algebraic expression,
Solution: (a) The product of x and y = x × y = xy multiplication and division are
written without their symbols
Trice of the product obtained = 3 × xy = 3xy ‘×’ and ‘÷’.
Note:
Now, 7 added to the thrice of the product of E.g., (a) x × y can be written as
x and y = 3xy + 7. x. y or xy
x
(b) Difference of the double of a and b = 2a – b (b) x ÷ y can be written as .
y
Thrice of the product of a and b = 3ab
Now, difference of the double of a and b added to the thrice of the product of a and
b = (2a – b) + 3ab

(c) The cost of x notebooks at `35 each = `35x
The cost of y pencils at `8 each = `8y
Therefore, the total cost of x notebooks at `35 each and the cost of y pencils at `8 each
= `(35x + 8y)

(d) Product of 4, b and c = 4bc and square of a = a 2
2
\ Required difference = a – 4bc

Life Skills
If there are x boys and y girls in your classroom and each child has to donate `10 for the Red Cross
Society of India to help the people who suffered from flooding in their region. How much amount will
your class collect for this Nobel cause? Ask the teacher about Red Cross society and how it works?

Practice Time 5C

1. Look at the following and answer the questions:
(a) (b)
x cm 4 cm 3 cm
x cm
................................... ...................................
What is the length of the knife? What is length of the handle of the screwdriver?

(c) 2y (d)
4x
`5 per apple `2 per banana
What is perimeter of the notebook? ................ If there are x apples and y bananas in the
What is the area of the notebook? ................ baskets. What is the total cost of the fruits
altogether? ................

Mathematics-7 110