Question

Hi, I need help.

Answer 1

Answer:

B, 24 (second answer choice)

Step-by-step explanation:

4r+7s=23

r-2s=17

8r+14s=46

7r-14s=119

15r=165

r=11

11-2s=17..........by putting value of r in ii

-2s=17-11

2s= -6

s= -3

3r+3s=3*11+3(-3) you get this by putting values of r and s

       =33-9

       =24    (B)

Answer 2

Answer:  B) 24

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Explanation:

Add the left hand sides of the two equations to get (4r+7s)+(r-2s) = 5r+5s

Do the same for the right hand sides of the two equations 23+17 = 40

After adding the equations, we end up with 5r+5s = 40 which is the same as 5(r+s) = 40

Next, divide both sides by 5 to lead to r+s = 8

Finally, multiply both sides by 3 to end up with 3(r+s) = 24 which is the same as 3r+3s = 24

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An alternative is to solve r-2s = 17 for r to get r = 2s+17. Then plug this into 4r+7s = 23 getting 4(2s+17)+7s = 23. This solves to...

4(2s+17)+7s = 23

8s+68+7s = 23

15s+68 = 23

15s = 23-68

15s = -45

s = -45/15

s = -3

Which means,

r = 2s+17

r = 2(-3)+17

r = 11

and therefore,

3r+3s = 3(-3)+3(11) = -9+33 = 24