group of 14 child some 9yr old and rest 11yr old

Question

When age of the 14 children are add togethertotal is 138yrs, and i is asked that you solve the number of 9 year olds there are? There re 8 9 year olds but how do you form an equation to solve this?

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Answer 1

you need to solve this system of two equations:

let's x= the number of 9-year"s, and y= the number of 11 year's

x+y=14

9x+11y=138

use the substitution method or the elimination method,

http://www.khanacademy.org/math/algebra/systems-of-eq-and-ineq/fast-systems-of-equations/v/solving-systems-of-equations-by-elimination

and you will get x=8, y=6