Skoool Kerala

Writing Expressions from Statements

We can use the rules of simplifying to write down an expression from a statement.

Examples:

John has m sweets and Peter has y sweets. How many sweets have they altogether?

They have m + y sweets.

These are unlike terms, so we cannot simplify this answer. It is written as an expression.


Jane has 5 more sweets than John. How many sweets does Jane have?

Jane has m + 5 sweets. (Unlike terms)


Bill has twice as many sweets as Peter. How many sweets does Bill have?

Bill has 2 x y = 2y sweets (Can be simplified to 2y by leaving out the multiply sign.)


Tim has half the number of sweets that John has. How many does Tim have?

Jill has four less sweets than John.

Jill has m – 4 sweets. (Unlike terms)

 

Making Equations

More information can be given in order to make an equation.

Example 1:  I multiply a number by 3 and then add 5. If the answer is 32, what was the number?

Let the number be y.

Three times the number = 3y

Add 5 = 3y + 5

Example 2: The length of a rectangle is (m + 3) cm and the width is 5 cm. If the area is 50 cm², find the length of the rectangle.

Area = Length x Width
   50 = ( m + 3) x 5

We need the brackets to show that the three and the m together make the length.

The equation is 5( m +3) = 50

We can solve this equation to find m.

Example 3: The length of a rectangle is t cm. The width is 5 cm less than the length. If the perimeter is 50 cm, make an equation in t and solve to find the length and width of the rectangle.

Length = a
Width = a – 5
Perimeter = a + a + (a - 5) + (a -5 )