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Samantha has 70 dollarsThe amount she has is just right for 4kg of fish and 3kg of prawns. Samantha bought 3kg of fish and 4kg of prawnsHer change was 3.50How much is 1kg of prawn?

User Matt Handy
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1 Answer

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Assume that the price of 1 kg fish is x and 1 kg of prawns is y

∵ She has 70 dollars

∵ The price of 4 kg fish and 3 kg prawns will be the total money with her

4x + 3y = 70 ====== (1)

∵ She bought 3 kg fish and 4 kg prawns

∵ She has 3.50 dollars left

→ That means the price of them = 70 - 3.50 = 66.5 dollars

3x + 4y = 66.5 ===== (2)

Now we have a system of the equations to solve it and find the value of y

Multiply the first equation by -3 and the 2nd equation by 4

∵ -3(4x) + -3(3y) = -3(70)

-12x - 9y = -210 ===== (3)

∵ 4(3x) + 4(4y) = 4(66.5)

12x + 16y = 266 ===== (4)

Add equations (3) and (4)

∴ 7y = 56

Divide both sides by 7 to find y

y = 8

The price of 1 kg of prawn is $8

User Roerjo
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