First algebra and simple equations · Usually met around P5
Algebra: letters for numbers
3x = 3 × x: substitute, then work it out.
How to do it
Method
3x = 3 × x: substitute, then work it out
x = 4: 3x + 2 = 3 × 4 + 2 = 14
Another way
Read it in words
3 times x, plus 2: 12 + 2 = 14
In full
A letter can stand for a number. 3 × x is written 3x (the number first, no × sign), and x ÷ 3 can be written x/3. To find an expression's value, put the number in place of the letter and work it out. When x = 4, 3x + 2 = 3 × 4 + 2 = 14. Careful: 3x is not a number in the thirties; it is 3 times x. Or read the expression in words first: 3x + 2 is “3 times x, plus 2”; 3 times 4 is 12, plus 2 is 14.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
When y = 46, the value of y + 5 is □
Show the answer and working
Answer: 51
Put 46 in place of y: 46 + 5 = 51.
Example 2
When n = 64, the value of n ÷ 8 + 9 is □
Show the answer and working
Answer: 17
Divide, then add: 64 ÷ 8 = 8, 8 + 9 = 17.
Example 3
When x = 4, the value of 7x is 74.
True or false?
Show the answer and working
Answer: False
7x = 7 × x = 7 × 4 = 28.
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