Which of the following numbers is 13 less than negative five? Circle your answer. The options are negative 18, eight, negative eight, and 18.
So straight away, we look at the question. And we can see that what we want to do is find a number that is 13 less than negative five. And it’s this less than part which is really useful because therefore we know the number cannot be more than negative five. So straight away, we can rule out the two positive answers eight and 18. That’s because if they’re positive and negative five is a negative number, then they cannot be less than negative five.
Well, now if we want to consider which one of the final two answers it’s going to be, we can see what is 13 less than negative five. Well, if we start at negative five and we get five less than negative five, we’re gonna get to negative 10. Well, therefore, we’ve actually ruled out negative eight because we’ve only gone five less and we’ve already gone past negative eight. So therefore, we can rule that out. So the answer is gonna be negative 18. But let’s show that it is.
It’s also worth noticing here that I said it’s five less. If we’re saying less than, it means that we’re subtracting. And we’re moving left on our number line. Well, now if we go 10 less than negative five, it means subtracting or moving left 10 from negative five. We get to negative 15, so still not 13 less. Well, if we subtract three more, so we’re gonna go to 13 less, then this is three values less than negative 15. So we got negative 16, negative 17, negative 18.
So therefore, the correct answer is negative 18 cause we can say that negative 18 is 13 less than negative five. And if we wanted to check this, we could go the other way and add 13 onto negative 18. And it will take us to negative five.