Answer: x = 15 ; y = 5
Explanation:
x + y = 20
x - y = 2*y
x = 20 - y
20 - y - y = 2*y
20 - 2*y = 2*y
- 2*y - 2*y = -20
- 4*y = -20
y = -20 / -4
y = 5
x + 5 = 20
x = 20 - 5
x = 15
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