Question

73. BUYING Suppose that you have a $129 credit on your account
at Amazon.com, and you want to spend it all on sale CDs at $10
cach, sale DVDs at $12 each, and sale books at $7 each. If you buy
13 items total, how many will you buy of each?​

Answer 1

buy of each in different cases CD = 1   DVD  = 7    Books = 5  or CD = 6   DVD = 4    Books = 3   or CD = 11   DVD = 1     Books = 1

Step-by-step explanation:

Let say CD bought  = C

Amount spends on CD = 10C

Let say DVD bought  = D

Amount spends on DVD = 12D

Let say Book Bought = B

Amount spend on Book  =  7B

C + D + B  = 13

10C + 12D  + 7B  = 129

10 C + 12D + 7(13 - C - D) = 129

=> 3C + 5D  = 38

using Hit & Trial

C = 1   D  = 7    B = 5

C = 6   D = 4    B = 3

C = 11   D = 1     B = 1

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