Question 1205779
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There are 5c, 10c, and 20c coins in Joel's wallet in the ratio of 2:6:7 respectively. 
If he takes out half the number of 5c and half the number of 10c coins they would make up $4.20
(a) How many 20c coins in his wallet.
(b) How much money does he have altogether
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            I changed the first line in your post, in order for 
            the time forms be consistent in all parts of the post.



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According to the problem, there are 2x of 5c coins; 6x of 10c coins and 7x of 20c coins,
where x is the common measure of these different quantities.


Half of 2x 5c coins is x 5c coins; half of 6x 10c coins is 3x 10c coins.
Their total is $4.20, or 420 cents

    5x + 10(3x) = 420  cents.


Simplify and find x

    5x + 30x = 420

      35x    = 420

        x    = 420/35 = 12.


Now we are in position to answer the problem's questions.


(a)  The number of 20c coins in his wallet is 7x = 7*12 = 84.

(b)  The total money in his wallet is  5*(2x) + 10*(6x) + 20*(7x) = 5*(2*12) + 10*(6*12) + 20*(7*12) = 2520 cents or $25.20.
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Solved.