Two dice A and B are rolled. Let the numbers obtained on A and B be α and β respectively. If the…

Two dice A and B are rolled. Let the numbers obtained on A and B be α and β respectively. If the variance of α-β is pq, where p and q are co-prime, then the sum of the positive divisors of p is equal to

  1. 72
  2. 36
  3. 48
  4. 31

Solution

Given that variance of α-β is pq

α1, 2, 3, 4, 5, 6

β1, 2, 3, 4, 5, 6

α-β=0 (6 case)

α-β=-1 (5 case)

α-β=-2 (4 case)

α-β=-3 (3 case)

α-β=-4 (2 case)

α-β=-5 (1 case)

α-β=1 (5 case)

α-β=2 (4 case)

α-β=3 (3 case)

α-β=4 (2 case)

α-β=5 (1 case)

Mean =0

We know that variance =i=1nfixi-x2i=1nfi

Variance=σ2=02×6+2×12×5+2×22×4+2×32×3+2×42×2×52×136

=236×5+16+27+32+25=10518=356

 p=35

Sum of divisors of p=1+5+7+35=48

Option 3 is correct.

Asked in: JEE Main 2023 (12 Apr Shift 1)

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