Aptitude - Surds and Indices - Discussion
Discussion Forum : Surds and Indices - General Questions (Q.No. 5)
5.
If 3(x - y) = 27 and 3(x + y) = 243, then x is equal to:
Answer: Option
Explanation:
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.
Discussion:
21 comments Page 3 of 3.
Sri said:
4 years ago
1 .3^(x - Y ) = 27.
3^(x - Y ) = 3^3.
Base are equal.
So,
(x - Y ) = 3 --------------------> 1.
2. 3^( x + y ) = 243.
3^( x + y ) = 3^5.
Base are equal,
So,
( x + y ) = 5 --------------------> 2.
Solve 1 & 2.
X + Y = 3.
X - Y = 5.
----------------------
2x. = 8.
X = 8/2.
So,
X = 4.
3^(x - Y ) = 3^3.
Base are equal.
So,
(x - Y ) = 3 --------------------> 1.
2. 3^( x + y ) = 243.
3^( x + y ) = 3^5.
Base are equal,
So,
( x + y ) = 5 --------------------> 2.
Solve 1 & 2.
X + Y = 3.
X - Y = 5.
----------------------
2x. = 8.
X = 8/2.
So,
X = 4.
(7)
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