2
algebra

Solve by elimination: {3x+4y=275x2y=11\begin{cases} 3x + 4y = 27 \\ 5x - 2y = 11 \end{cases}

A

(4,154)(4, \frac{15}{4})

B

(5,3)(5, 3)

C

(3,4.5)(3, 4.5)

D

(6,2.25)(6, 2.25)

Correct Answer: B

Choice B is the correct answer. To eliminate yy, multiply the second equation by 2.

Step 1: Multiply the second equation by 2: 10x4y=2210x - 4y = 22

Step 2: Add to the first equation: (3x+4y)+(10x4y)=27+22(3x + 4y) + (10x - 4y) = 27 + 2213x=4913x = 49x=4913x = \frac{49}{13}

Non-integer. - First: 3(5)+4(3)=15+12=273(5) + 4(3) = 15 + 12 = 27

  • Second: 5(5)2(3)=256=19 eq115(5) - 2(3) = 25 - 6 = 19 \ eq 11

Step 1: Multiply second by 2: 10x4y=3810x - 4y = 38

Step 2: Add: 13x=6513x = 65x=5x = 5

Step 3: Substitute: 3(5)+4y=273(5) + 4y = 2715+4y=2715 + 4y = 27y=3y = 3

** 💡 Strategic Tip: Multiplying by 2 turned the 2y-2y into 4y-4y to match the +4y+4y in the first equation.

Choice A is incorrect because3(4)+4(154)=12+15=273(4) + 4(\frac{15}{4}) = 12 + 15 = 27 ✓, but 5(4)2(154)=207.5=12.5 eq195(4) - 2(\frac{15}{4}) = 20 - 7.5 = 12.5 \ eq 19.

Choice C is incorrect because3(3)+4(4.5)=9+18=273(3) + 4(4.5) = 9 + 18 = 27 ✓, but 5(3)2(4.5)=159=6 eq195(3) - 2(4.5) = 15 - 9 = 6 \ eq 19.

Choice D is incorrect because3(6)+4(2.25)=18+9=273(6) + 4(2.25) = 18 + 9 = 27 ✓, but multiplication in second fails.