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Math for 7th grade
Adding and subtracting expressions: positive and negative numbers, longer sums like 7 − 8 + 9, minus a minus, like terms (7a + 8b − 9c + 3a − 3b = 10a + 5b − 9c), brackets and word problems. Worked examples on every page, and quizzes that make new exercises every time, with the working shown for every mistake.
- 8 topics
- 10 quizzes and flashcard sets
- 11 recorded audio clips
- free, in the browser or the Android app
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What is inside
Adding and subtracting expressions From 7 − 8 + 9 to 7a + 8b − 9c + 3a − 3b
Adding and subtracting looks easy until minus signs and letters join in. In this chapter you go step by step from 7 - 8 + 9 to 7a + 8b - 9c + 3a - 3b, and by the end both will take you a few seconds.
Practice: Chapter test: adding and subtracting expressions
- Positive and negative numbers The number line: adding moves right, subtracting moves left
Numbers below zero are everywhere: a winter night of −5 °C, the lift going down to floor −2, or a bank account in the red. A negative number has a minus in front of it: -3 is read “minus three”.
Practice: Positive and negative numbers
- Longer sums: 7 − 8 + 9 Left to right, or the pluses together and the minuses together
With more than two numbers, like 7 - 8 + 9, go from left to right, one step at a time. Every sign belongs to the number right after it.
Practice: Longer sums
- Minus a minus 6 − (−5) = 6 + 5
Sometimes the number you add or take away is negative itself. Then it gets brackets so the two signs don't bump into each other: 6 - (-5).
Practice: Minus a minus
- Terms and like terms Coefficients, letters, and which terms belong together
In algebra, letters stand for numbers: ones we don't know yet, or ones that can change. 3a means 3 · a, three a's: a + a + a.
Practice: Terms and like terms · Words to know · flashcards
- Collecting like terms 7a + 8b − 9c + 3a − 3b = 10a + 5b − 9c
Collecting like terms means putting each family together by adding up their coefficients. 3a + 5a = 8a, just like 3 apples and 5 apples make 8 apples. This is called simplifying an expression.
Practice: Collecting like terms · Collecting like terms · challenge
- Adding and subtracting brackets (3a + 2b) − (a − 4b) = 2a + 6b
Now you add and subtract whole expressions, like (3a + 2b) - (a - 4b). It takes two steps: first take the brackets away, then collect the like terms.
Practice: Adding and subtracting brackets
- Expressions in real life Perimeters, money, ages and buses
Expressions are a short way to write down things whose exact numbers we don't know yet. Write what you know with a letter, then simplify.
Practice: Expressions in real life
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