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1. If 3(x - y) = 27 and 3(x + y) = 243, then x is equal to:

Solution:
3x - y = 27 = 33     ⇔     x - y = 3 ....(i)
3x + y = 243 = 35     ⇔     x + y = 5 ....(ii)
On solving (i) and (ii), we get x = 4.

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