3 mistakes learners make with collecting like terms, each one named and explained.
Only terms built from exactly the same letters can be combined, because only those count the same thing.
5a + 3b - 2a + b is answered as 7a + 4b, with the 2a added rather than taken away.
The terms are collected by scanning for matching letters, and the sign in front of each one is a separate thing to remember.
Question. 5a - 2a
A common answer. 7a
The answer. 3a
Why. The minus belongs to the 2a, so there are five a s and two are taken away.
Every term travels with the sign in front of it. Circle the signs before you collect.
3a + 2b is answered as 5ab.
The instruction says simplify, and one term looks a great deal tidier than two.
Question. 3a + 2b, with a = 10 and b = 1
A common answer. 5ab, which works out as 50
The answer. 32
Why. 3 lots of 10 and 2 lots of 1 is 32, so 5ab cannot be the same expression.
Only terms built from exactly the same letters combine. Sometimes the tidy answer is the one you started with.
5a + 3b - 2a + b is answered as 3a + 2b, because the b on its own was not counted.
A term with no number in front looks like it has no number, rather than a hidden one.
Question. 3b + b
A common answer. 3b, because the lone b adds nothing
The answer. 4b
Why. A letter on its own means one of them, so 3b and one more b is 4b.
A letter standing alone always carries an invisible 1. Write it in until it is automatic.
WAJD spots these patterns in your child's answers and names the one behind their wrong answers, instead of just marking them wrong.