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Question
Arnab needs to pay Rs.210 for his dinner. He has an unlimited supply of Rs 2, Rs 5 and Rs 10 notes; in how many ways can he pay?
Options:
A .  210
B .  253
C .  231
D .  None of these
Answer: Option A
:
A
Equation become like 2x + 5y + 10z = 210, where
X should be a multiple of 5 and Y should be a multiple of 2. So, we can take X and Y as 5P and 2Q respectively.
Now equation becomes:-
10P + 10Q + 10Z = 210;
P + Q + Z = 21
where P, Q and Z are non-negative integers. Number o f solutions of the given equation is 23C2 = 253. Option (b).

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