Question Video: Finding an Unknown Number in Two Numbers given Their Average Using Linear Equations

If the average of two numbers is 65, where one of them is 60, find the other number.

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Video Transcript

If the average of two numbers is 65, where one of them is 60, find the other number.

To calculate the mean or the average, we add up all the numbers and divide by how many they are. Firstly, we work out the sum and then we divide by the number of terms: the sum of 𝑥 divided by 𝑛. In this case, we have two numbers 60 and 𝑥. As there are just two of them, we need to divide by two. 𝑛 equals two.

And we know that the average or mean of the two numbers is equal to 65. This gives us an equation 60 plus 𝑥 divided by two equals 65. Multiplying both sides of the equation by two gives us 60 plus 𝑥 equals 130.

Our next step is to subtract 60 from both sides of the equation, which leaves us with 𝑥 equals 70 as 130 minus 60 is equal to 70. This means that the other number is equal to 70. The average of 60 and 70 is 65. When dealing with just two numbers, we can also work out the average by finding the midpoint or halfway between the two numbers. Halfway between 60 and 70 is 65.

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