Circle two numbers that add together to equal 0.25. And then we’re given four possible numbers to circle: 0.05, 0.23, 0.2, or 0.5.
The question asks us to find two numbers, that when we add them together give a total of 0.25. In other words, what plus what equals 0.25? Let’s look carefully at our four numbers that we’ve been given to choose from. Now the way that this question has been written, we need to be very careful about which numbers we choose.
We may think because 23 and two make 25, 0.23 and 0.2 will make 0.25. We may think that because 0.25 has got a two and a five in it that it’s the total of 0.2 and 0.5, or even 0.2 and 0.05. It would be very easy to just guess at the answer and end up getting the wrong answer as a result. Only one of these answers is correct. The key to solving this problem is to use our knowledge of place value to help.
So let’s quickly sketch a place value grid to help us. We’re going to need three columns: our ones, tenths, and hundredths. The number 0.25 is made up of zero ones, two tenths, and five hundredths. Let’s write down our four possible choices underneath to help us understand them: 0.05, 0.23, 0.2, and 0.5.
Notice that each of our numbers has zero ones. So where are we going to find the two tenths and the five hundredths that we need? Are there any numbers that we can see won’t add together to make two tenths? Or we can see that 0.5 has got five tenths. This is larger than 0.25. And so we can cross off this number.
Two out of the remaining numbers have two tenths already, 0.23 and 0.2. As well as two tenths, 0.25 has five hundredths. And we can see that our first number 0.05 also has five hundredths. And because it has zero tenths, we can add it to a number with two tenths and no hundredths to give us our number with two tenths and five hundredths. Because we’ve set up the numbers using a place value grid, we could even do a quick vertical addition to check our answer.
Five hundredths plus no hundredths equals five hundredths. No tenths plus two tenths equals two tenths. Don’t forget the decimal point. And then zero ones and zero ones remains zero ones. And so the two numbers that add together to equal 0.25 are two tenths or 0.2 and five hundredths or 0.05.
The numbers that we were given in this question were such that it would be very easy to rush in and make a mistake. Instead of guessing, we decided to use our knowledge of place value to help. We sketched a place value chart to help. And this helped us to think very carefully about the value of each digit and so to find the two numbers that equal 0.25.