One number is 4 less than 3 times a second number. If 3 more than two times the first number is decreased by 2 times the second number, the result is 11. Use the substitution method. What is the first number?

1 Answer
Jun 16, 2016

n_1=8n1=8
n_2=4n2=4

Explanation:

One number is 4 less than -> n_1=?-4n1=?4
3 times " ........................."->n_1=3?-4 .........................n1=3?4
the second number color(brown)(".........."->n_1=3n_2-4)..........n1=3n24
color(white)(2/2)22

If 3 more " ..........................................."-> ?+3 ...........................................?+3
than two times the first number" ............"->2n_1+3 ............2n1+3
is decreased by "..................................."->2n_1+3-?...................................2n1+3?
2 times the second number" ................."->2n_1+3-2n_2 .................2n1+32n2
the result is 11color(brown)(" ....................................."->2n_1+3-2n_2=11) .....................................2n1+32n2=11

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color(white)(.)n_1=3n_2-4.n1=3n24 .....................Equation (1)
2n_1+3-2n_2=112n1+32n2=11...........Equation (2)

Substitute for n_1n1 in equation (2) using equation (1)

color(brown)(2n_1+3-2n_2=11)" "color(blue)( ->2(3n_2-4)+3-2n_2=11)2n1+32n2=11 2(3n24)+32n2=11

Multiplying out the brackets

6n_2-8+3-2n_2=116n28+32n2=11

4n_2-5=114n25=11

Add 5 to both sides

4n_2=164n2=16

Divide both sides by 4

" "color(green)(n_2=4) n2=4
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Substitute n_2=4n2=4 into equation (1)

n_1=3(4)-4n1=3(4)4

n_1=12-4n1=124

" "color(green)(n_1=8) n1=8
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Check: One number is 4 less than 3 times the second number

8=3(4)-4=88=3(4)4=8 confirmed!