Aptitude - Simplification - Discussion

In this a to b represents the equation x-10 = y+10.

In this b to a represents the equation x+20 = 2(y-20).

Solving 2 equation we get the answer.

First read the question 1 time.

A = x; B=y.

'A' sent 10 students to 'B' => x-10 = y+10.

We solve the equation as x-y = 20. It becomes equation 1.

Then 'B' sent 20 students to 'A' => x+20 = 2(y-20).

The number of students in 'A' is double the number of students in 'B'.

x+20 = 2(y-20).

We simply the equation as x+20 = 2y-40.

Bring 2y-40 to left side,

x-2y+20+40 = 0.

We solve the equation as x-2y = -60.......equation 2.

Now solve equation 1&2,

x-y = 20.

x-2y = -60.
_____________.

y = 80.

Now we substitute y = 80 in equation 1 or 2.

x-80 = 20.

x = 100.

First of all.

Let the no of students in room A = x; B=y.

A sent 10 students to b....i.e. x-10 = y+10.

Take y to left side and -10 to right side.

It becomes x-y = 20.....equation 1.

Then B sent 20 students to A....i.e. 2x+20 = 2(y-20).

In questions it is mentioned that after sending 20 students A have Double no of students.

That's why we are using 2 here now write equation as,

x+20 = 2(y-20).

x+20 = 2y-40.

Bring 2y-40 to left side,

x-2y+20+40 = 0.

We can write it as,

x-2y = -60.....equation 2.

Now solve equation 1&2,
x-y = 20.
x-2y = -60.
_____________
y = 80.

Now substitute y = 80 in equation 1 or 2.

x-80 = 20.

Therefore x = 100.

Hope you understand this @RAMA.

If you don't mine, somebody please explain this in clear cut. First of all I can't understand the question.

x-y = 20 ------------(1).
x-2y = -60 ------------(2).

Solving (1) - (2),

x -y = 20----(1).
x -2y = -60----(2).
---------------
y = 80.
---------------
(If you want to solve two equations in any problem you must change sing of (2)nd equation without fail.)

Now you substitute the y value in (1)st or (2)nd equations as you like then you will get the value of x as 100.

x - y = 20-----(1).
y = 80.

so, x - 80 = 20.
x = 20+80.
x = 100.

Now you got it @Selvi.