Seven persons A, B, C, D, E, F and G are standing in a straight line. D is to the right of G. C is between A and B. E is between F and D. There are three persons between G and B. Who is on the extreme left?

Krishna is to the right of Samy.
There is no person between Samy and Krishna.
There is no person between Vaani and Sheela.
So, Saroj is sitting to the left of Samy.

According to question,
We can draw a figure , in which Shekhar is to the immediate right of Dhanush. Bala is between Basha and Dhanush. David is at the extreme right end of the row.
As shown in figure , Dhanush is standing in the middle.
Sitting arrangement :-

According to question,
We can draw a figure , It is given in the question that Sudha is not next to Tapti. This condition must be ommittted to solve the question. As shown in figure , Padma is in the middle.
Sitting arrangement :-

According to question ,
A is 7th from the left and B is 9th from the right.
After interchanging their positions ,
Now A becomes 11th from the left.
? Total number of people in the row = A's position + B's position - 1
Total number of people in the row = 11 + 9 ? 1 = 19

Draw a figure on the basis of above given question ,
D is between A and C. B is just right of C but left of F. E is not at the right end.
From figure , It shows that F is at the right end.
Sitting arrangement :-

Draw a figure on the basis of above given question ,
A and B belong to Ruby House, while the rest belong to Emerald House. D and F are tall, while others are short. C and D are wearing glasses while others are not wearing.
D is from Emerald House. She is tall. She wears glasses.
sitting sequence :-

According to question,
We can draw a figure , in which Mohan is between Balu and Raju and Raju is to the immediate right of Praveen and Amith is to the right of Balu.
As shown in figure , Amith is in extreme right end .
Sitting arrangement :-

According to question,
Malini is behind Anjana, but in front of Gayathri. Meena is in front of Shena, but behind Gayathri.
It is clear that , Meena is second from the last.
Standing arrangement :-

According to question,we have
John's position = 16th from the left
Johnson's position = 8th from the right
After interchanging their positions ,
John's position = 33rd from left
? Total number of students = John's position + Johnson's position - 1
Total number of students = 33 + 8 ? 1 = 40

According to question,
We can draw a figure , in which P is to the left of M and to the right of O. R is sitting to the right of N, but to the left of O.
From given figure it is clear that , O is sitting in the middle.
Sitting arrangement :-