Answered

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A library buys 50 books. Some cost K5 and
others cost K7.If the library spent K290 in
all, how many books costing K5 did it buy?​

Sagot :

Parrain

Answer: 30 books

Explanation:

Assume the books that cost K5 is x and the books that cost K7 is y.

50 books were purchased so the first formula is:

x + y = 50

They added up to K290 so the second formula is:

5x + 7y = 290

x + y = 50

5x + 7y = 290

x + y = 50

y = 50 - x

Substitute that into the second formula as y:

5x + 7(50 - x) = 290

5x + 350 - 7x = 290

5x - 7x = 290 - 350

-2x = -60

x = -60/-2

x = 30 books costing K5

y = 50 - x

= 50 - 30

= 20 books costing K7

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