Aptitude - Simplification - Discussion

When 20 students sent from B to A,

Then A become twice then of B.

Thats The Reason We take 2 in the second step.

Please explain me, how to solve (i) & (ii) and how get x=100 & y=80?

To solve equations:

(A part) (B part)
x + 20 = 2(y - 20)
20 candidates are sent from B to A,so we are adding 20 to x,and because we are sending 20 students to A it gets doubled(A=2B).
And
For solving equations just subtract both.

x - y = 20 .... (i)

x - 2y = -60 .... (ii)

You will get y=80 and then substitute in eq(i) you will get x=100.

They said the number of students in A is double the number of students in B. We should multiply A by 2 instead of multiplying B by 2. Why we are multiplying A by 2? Please tell me.

10 students moving from A to B


( decrease 10 from A & add 10 to B)
Then, A - 10 = B + 10 A - B = 20 .... (i)

20 Students moving B to A.(Note: After deducting 20 from B , A will be double) .

A + 20 = 2(B - 20)

A - 2B = -60 .... (ii)


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Solving (i) and (ii) we get: A = 100 , B = 80.

The required answer A = 100.

I didn't understand Solving (i) and (ii) we get: x = 100, why = 80. How?

Amigos..

Then the number of students in A is double the number of students in B.

Just use is equal to "=" instead of "is" After A and then think of it.

Easy isn't it.

Take these two cases individually let us look first through options 1st option is 20 so to apply both conditions is not possible so come to 80 so given if 10 people are sent to b then people in both class rooms are same so definetly b will be 60.

So again now apply second condition individually so by sending 20 people 4rm b A is twice that of B so this condition is not satisfied so now take 100 and check then both conditions satisfy and hence ans is 100

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.

Can you explain by assuming a = 100?