In this question, we’ve got to use mental methods to solve the equation 𝑥 minus
twenty-seven equals five.
And we could solve this using inverse operations, and just balance the equation
algebraically on paper. So that would mean writing 𝑥 minus twenty-seven equals five. And then using the
inverse operation of taking away twenty-seven, so that’s adding twenty-seven, in order to
eliminate for that from the left-hand side. But if we did that to the left-hand side, I’m
gonna have to add twenty-seven to the right-hand side, to get those t- two things to balance
Now looking at this, on the left-hand side here we’ve got 𝑥 minus twenty-seven
and then I’ve got to add twenty-seven. So if I add twenty-seven and take away twenty-seven, I’m just gonna end up back with 𝑥. So on the left-hand side, I’ve just got 𝑥, and
on the right-hand side, I’ve got five plus twenty-seven. Well that’s equal to thirty-two.
Well that’s all well and good, but we were actually asked to solve this using
mental methods, not written methods. So let’s interpret the equation. 𝑥 minus twenty-seven
equals five, means something take away twenty-seven equals five. So I need to think, what number is five greater than twenty-seven, so that when
I take away twenty-seven from it, I get left with five? Well I can picture the number line in my head, and the number that’s five bigger
than twenty-seven is thirty-two.
So no matter which method I use, I get the answer thirty-two.