136
Equations
Textbook: Part 4, lesson 127, pp. 24–25
GoalSolve equations with an unknown minuend or subtrahend, including ones with brackets.
New words
minuend · kamayuvchisubtrahend · ayriluvchidifference · ayirmaunknown · noma’lum
Explanation
To find an unknown minuend, add the subtrahend to the difference: x − 612 = 321, x = 321 + 612 = 933. To find an unknown subtrahend, subtract the difference from the minuend: 541 − x = 215, x = 541 − 215 = 326. With brackets, calculate inside first: x − (141 + 123) = 245, x = 245 + 264 = 509.
Worked examples
541 − x = 215: x = 541 − 215 = 326. Check: 541 − 326 = 215.
x − 612 = 321: x = 321 + 612 = 933.
Class activity
“Equation masters”: each child writes an equation on a card. A neighbour solves it and checks the root by putting it back in. If it works, they say “Root found!”
Practice
1
541 − x = 215, x = ?
326
2
x − 612 = 321, x = ?
933
3
x + 284 = 351, x = ?
67
4
x − (141 + 123) = 245, x = ?
509
5
There were 284 m of thread for weaving a carpet. After using some, 97 m was left. How many metres were used?
187