# Aptitude - Surds and Indices - Discussion

### Discussion :: Surds and Indices - General Questions (Q.No.5)

5.

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

 [A]. 0 [B]. 2 [C]. 4 [D]. 6

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.

 Anu said: (Mar 22, 2011) How is (i) and (ii) solved and we get answer as 4??

 Anu said: (Jun 23, 2011) 2x=8; so x=4 ie.,(x+x)(-y+y) (3+5)

 Caroline said: (Sep 8, 2011) x - y = 3 x + y =5 --------------- 2x =8 Therefore, x = 4.

 Anju said: (Jul 19, 2013) 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.

 Samson said: (Sep 12, 2013) x-y = 3 x+y = 5 ________ 2x = 8 ________ 2x/2 = 8/2. x = 8/2. i.e x = 4.

 Mohammed Sani said: (Feb 19, 2014) We used simultaneous equation in solving that, we find for x then y before we can get the final answer.

 Arjun said: (Mar 27, 2015) How we can find the power? Is there any short technique by which we can find easily?

 Poonam Vaidya said: (Feb 19, 2016) I can't got this answer. Please anyone explain it in detail. Why we cut y?

 Hani said: (Apr 12, 2016) Why 2x is equal to 8?

 Shahjahan said: (Aug 15, 2016) (x - y) + (x + y) = 3 + 5, (x + x) - (y + y) = 8, 2x = 8, x = 4.

 Carol said: (Dec 3, 2016) How to solve the y? Don't get it, Please explain it clearly.

 Otuboye said: (Jan 2, 2017) Please, can you explain clearly how to solve the y?

 Ezekiel said: (Nov 21, 2018) 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.

 Olwa said: (Nov 25, 2018) 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.

 Ednan Malik. said: (Dec 30, 2018) (x-y) + (x+y) = 3+5, x+x - y-y = 8, 2x-0 = 8, 2x = 8, x = 8/2, x = 4.

 Ednan Malik said: (Dec 30, 2018) (x-y)+(x+y) = 3+5, (x+x-y+y) = 8, 2x+0 = 8, 2x = 8, x = 8/2, x = 4, Therefore x=4.

 Vikram Singh said: (Feb 1, 2019) 5x-5y = 3x+3y 5x-3x = 3y+5y 2x = 8y X ÷ y = 8 ÷ 2 so, X = 4,y = 1.

 Shrikanth said: (Aug 7, 2019) Thanks all for explaining it.

 Sri said: (Sep 15, 2021) 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.