Aptitude - Simplification - Discussion

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).
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y = 80.
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(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?

I can't understand the prasu explanation tell me clearly.

Based on the answer a=100 and b=80. They said that if 20 sent from a to b then.

A will become double of b.

So if 20 sent then a=120 and b=60 i.e. a is double of b.

Assume x,y

x-a, y-b

10 students from b-a. So x-b,then y+b

Now doubled

2(y-20) then both equation solved.

Tell me clearly. Please.

I can't understand the sentence "then the number of students in A is double the number of students in B" explain me.

Please help me solve this.

I don't know how 2 was came at step 2.

Please explain.