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 1 of 3.
Olwa said:
7 years ago
This is a simultaneous equation.
x-y= 3 ---> (i)
x+y=5 ---> (ii)
From eqn (i), we first make x the subject by adding y to both sides;
=> x-y+y=3+y,
=> x=3+y ---> (iii).
Substituting value of x from eqn (iii) in eqn (ii),we get
(3+y)+y=5,
=> 3+2y=5,
=> 3-3+2y=5-3,
=> 2y=2,
Therefore, y=1 ---> (iv).
Substituting eqn (iv) in eqn (iii),
=> x=3+1.
Therefore, X= 4.
x-y= 3 ---> (i)
x+y=5 ---> (ii)
From eqn (i), we first make x the subject by adding y to both sides;
=> x-y+y=3+y,
=> x=3+y ---> (iii).
Substituting value of x from eqn (iii) in eqn (ii),we get
(3+y)+y=5,
=> 3+2y=5,
=> 3-3+2y=5-3,
=> 2y=2,
Therefore, y=1 ---> (iv).
Substituting eqn (iv) in eqn (iii),
=> x=3+1.
Therefore, X= 4.
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)
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.
(3)
Anju said:
1 decade ago
3 (x-y) = 27.
x-y = 27/3.
x-y = 9 ----- (1).
3 (x+y) = 243.
x+y = 243/3.
x+y = 81 ----- (2).
(x+y) = 81.
(x-y) = 9.
-------------
2y = 72.
y = 72/2 = 36.
y = 36.
x-y = 9.
x-36 = 9.
x = 36/9.
x = 4.
x-y = 27/3.
x-y = 9 ----- (1).
3 (x+y) = 243.
x+y = 243/3.
x+y = 81 ----- (2).
(x+y) = 81.
(x-y) = 9.
-------------
2y = 72.
y = 72/2 = 36.
y = 36.
x-y = 9.
x-36 = 9.
x = 36/9.
x = 4.
EZEKIEL said:
7 years ago
The simultaneous equation as in;
x-y=3 x1.
x+y=-5 x-1.
y will be 0 which is always ignored after addition, we get;
2x=8.
where x =4.
x-y=3 x1.
x+y=-5 x-1.
y will be 0 which is always ignored after addition, we get;
2x=8.
where x =4.
Mohammed sani said:
1 decade ago
We used simultaneous equation in solving that, we find for x then y before we can get the final answer.
Arjun said:
1 decade ago
How we can find the power?
Is there any short technique by which we can find easily?
Is there any short technique by which we can find easily?
Ednan malik said:
7 years ago
(x-y)+(x+y) = 3+5,
(x+x-y+y) = 8,
2x+0 = 8,
2x = 8,
x = 8/2,
x = 4,
Therefore x=4.
(x+x-y+y) = 8,
2x+0 = 8,
2x = 8,
x = 8/2,
x = 4,
Therefore x=4.
(3)
Samson said:
1 decade ago
x-y = 3
x+y = 5
________
2x = 8
________
2x/2 = 8/2.
x = 8/2.
i.e x = 4.
x+y = 5
________
2x = 8
________
2x/2 = 8/2.
x = 8/2.
i.e x = 4.
(1)
Poonam vaidya said:
10 years ago
I can't got this answer.
Please anyone explain it in detail. Why we cut y?
Please anyone explain it in detail. Why we cut y?
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