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MBADream786
The number of positive integral solutions of the equation a+b+c+d+e = 30 is?
A.25173
B.23517
C.25731
D.23751
E.23518

So 30 has to be distributed amongst 5 sets a,b,c,d and e. As we are looking at positive integral solution, let us give 1 each to all 5.
Remaining now =30-5=25
So let us now add 4 partItions so that we can distribute these in 5 sets and then choose these 4 partitions
=> (25+4)C4=29*28*27*26/4!=29*7*9*13=23751

D
chetan2u Could you please explain what you mean by adding 4 partitions? I understood up to 30-25=5 Thanks
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Hi Jagwik
To distribute among 5 people(suppose a,b,c,d,e are people and we are distributing 30 toffees), we need to make four partitions.One after a, one after b, one after c, and one after d, hence Four.
Hope it helps.
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Hi Jagwik
To distribute among 5 people(suppose a,b,c,d,e are people and we are distributing 30 toffees), we need to make four partitions.One after a, one after b, one after c, and one after d, hence Four.
Hope it helps.

Yogananda

I'm struggling to understand the solution. If it is not incovenient, could you please explain how it is (25+4)C4? Thanks
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chetan2u
MBADream786
The number of positive integral solutions of the equation a+b+c+d+e = 30 is?
A.25173
B.23517
C.25731
D.23751
E.23518

So 30 has to be distributed amongst 5 sets a,b,c,d and e. As we are looking at positive integral solution, let us give 1 each to all 5.
Remaining now =30-5=25
So let us now add 4 partItions so that we can distribute these in 5 sets and then choose these 4 partitions
=> (25+4)C4=29*28*27*26/4!=29*7*9*13=23751

D
chetan2u Could you please explain what you mean by adding 4 partitions? I understood up to 30-25=5 Thanks

So, let the integers be represented by *, and partition by |.
We have **|*|*******|*****|**********
So above is a case where a has 2, b has 1, c has 6, d has 5 and remaining 11 in e.
We have 25* and 4 |, so total 29 and we have to choose 4 | out of them.
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chetan2u
MBADream786
The number of positive integral solutions of the equation a+b+c+d+e = 30 is?
A.25173
B.23517
C.25731
D.23751
E.23518

So 30 has to be distributed amongst 5 sets a,b,c,d and e. As we are looking at positive integral solution, let us give 1 each to all 5.
Remaining now =30-5=25
So let us now add 4 partItions so that we can distribute these in 5 sets and then choose these 4 partitions
=> (25+4)C4=29*28*27*26/4!=29*7*9*13=23751

D

chetan2u is there any way by which we could bypass the tedious calculation and choose an answer choice thereby saving time?
I did the unit digit calculation and got stuck between Option C and D
Curious to know how you would approach it
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chetan2u
MBADream786
The number of positive integral solutions of the equation a+b+c+d+e = 30 is?
A.25173
B.23517
C.25731
D.23751
E.23518

So 30 has to be distributed amongst 5 sets a,b,c,d and e. As we are looking at positive integral solution, let us give 1 each to all 5.
Remaining now =30-5=25
So let us now add 4 partItions so that we can distribute these in 5 sets and then choose these 4 partitions
=> (25+4)C4=29*28*27*26/4!=29*7*9*13=23751

D

chetan2u is there any way by which we could bypass the tedious calculation and choose an answer choice thereby saving time?
I did the unit digit calculation and got stuck between Option C and D
Curious to know how you would approach it

You are correct with units digit.
The other could have been to check the divisors.
Here 9 is a divisor, so the sum of digits should be divisible by 9. However, as luck would have it, the digits are exactly the same in C and D. The remaining factors 7, 13, 29 etc do not have a trick attached to it.

So, only way is to see division by 7.
25731=21000+4731=21000+4200+531=21000+4200+490+41....41 is not divisible by 7
23751=21000+2751=21000+2800-49....each term is divisible by 7
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