137
Equations
Textbook Part 4, pp. 54–55
GoalKnow that an equation is an equality where an unknown number is shown by a letter; write an equation from a picture.
New words
equation · tenglamaunknown · noma’lumx · x (iks)
Explanation
An equality in which one number is unknown is called an equation. The unknown is shown by a letter: x + 5 = 12. Before, we wrote “_ + 5 = 12” — now we put a letter in place of the gap.
Worked examples
78 first-graders chose porridge; 63 chose rice porridge: 63 + x = 78 → x = 78 − 63 = 15 chose wheat porridge.
Of 28 l of yoghurt, 16 l was left for lunch: 28 − x = 16 → x = 12 l was drunk at breakfast.
Class activity
“Hidden number”: the teacher lays a card face down (x) and writes “+ 4 = 11” next to it. Children find x, then the card is turned over.
Practice
1
Which is an equation: 5 + 3 = 8 or x + 3 = 8?
x + 3 = 8
2
The kitchen made 18 l of juice; 12 l is apple. How much is pear? Write an equation.
12 + x = 18, x = 6 l
3
12 dm + x = 42 dm. x = ?
30 dm
4
x + 5 = 12. x = ?
7