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 Question from Bernie, a parent: The average weight of a team of children is 50kg, Todd who weighs 56 kg then joins the team. The average weight of the new team is 51. How many children in the original team?

Hi Bernie,

If you knew the total weight of the team and the number of children on the team then you would find the average weight by dividing the total weight by the number of children. To say this algebraically let $T$ be the total weight of the children on the team in kilograms and $n$ be the number of children on the team then

$\frac{T}{n} = 50 \mbox{ kilograms}$

or

$T = 50 \times n.$

After Todd joins the team what is the total weight of the children on the team? What is the new number of children on the team? The new average weight is 51 kilograms so this gives you a second equation in $T$ and $n.$ Solve these equations for $n.$

Penny

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