The problems are all the same sort: add the side lengths to find the perimeter, make use of the information you have about the perimeter to solve the resulting equation, go back and use that solution to find the side lengths.
1. s + (s+5) + (s-3) = 35
... 3s +2 = 35
... s = (35 -2)/3 = 11
Side lengths are s=11, s+5=16, s-3=8. Perimeter is given as 35, but we can check to make sure: 11 + 16 + 8 = 35.
2. s +3s +2s = 72
... 6s = 72
... s = 72/6 = 12
Side lengths are: s=12, 3s=36, 2s=24. Perimeter is given as 72, but we can check: 12 +36 +24 = 72.
3. s +(s-7) +4s = 47
... 6s -7 = 47
... s = (47 +7)/6 = 9
Side lengths are: s=9, s-7=2, 4s=36. Perimeter is given as 47, but can be verified as 9 +2 +36 = 47.
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Please be aware that the "triangles" in problems 2 and 3 are not real triangles. The "triangle" of problem 2 will look like a straight line of length 36. Its area will be zero.
The "triangle" of problem 3 cannot be drawn, as the ends of the legs cannot be made to meet. The sum of the shortest two legs (9+2=11) should be longer than the longest leg, but is not. (11 is not greater than 36)
That is, problems 2 and 3 are problems in math only; not problems in geometry.
