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)
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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
