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Ans given: 100

Lets take an example, Below are three instances of table with ratio of tuples equal to the original relation.

A B C
Y  Y  L
P  Q  M
C  D  N
X  Z  O

C D E
L  Z  A
M  Z  A
N  Z  A
L  Z  B
M  Z  B
O  Z  B

E F
A  Z
B  Z

If we join tem in any way the resulting table will have 6 tuples
We can thus conclude that P join Q join R will result in 300 tuples.

A B C D E F
Y  Y  L  Z  A  Z
Y  Y  L  Z  B  Z
P  Q  M  Z  A  Z
P  Q  M  Z  B  Z
C  D  N  Z  A  Z
X  Z  O  Z  B  Z

selected
NO...if we join Q(CE) and R(E) then we can get 300 tuples.

Then with P....300 should be answer.
Suppose CE attributes have tuples as:

ab

ac

bb

bc

And EF attributes have tuples as:

bg

ct

Then the join of these results in tuples

abg

act

bct

bbg

Here we're getting the tuples from relation having maximum tuples. Correct me if I'm wrong @Rakesh
Thanks guys for correcting me, updated the answer with an example.
All credits to vaishali :)

Ths is wrongly framed question. They havent stated maximum or minimum.

If minumum, then its 0.

If maximum, then 300 tuples

^ how min = 0 ??

If one of C or E for all touple of relation Q is null ??
Consider the tables here:

Table P

-------------------------------------------------

A          B       C

------------------------------------------------

1         1         1

2         2         2

.

.

200    200      200

Table Q

------------------------------------

C            D              E

-------------------------------------

201         201            201

202         202            202

.

.

500         500            500

Table R

------------------------------------------------

E                    F

------------------------------------------------

501              501

502              502

.

.

600              600
..........
@Vijay. I dont think that for relation Q, one of C or E can be null.
I thought, C in Q is foreign key pointng to C in P and similarly E in Q referring to E in R.

So, we should not consider foreign key even if there is common attribute between two relation unless it is mentioned explicitly. ??
@Vijay. Yes. We shouldn't consider unless explicitly stated because we have satisfied the conditions they have given.
But, if options are given, we need to consider that C is foreign key in Q   :P
....
maximum tupples can be 200.