Consider two sets $A$ and $B$, each containing three numbers in A.P. Let the sum and the product of the…

Consider two sets $A$ and $B$, each containing three numbers in A.P. Let the sum and the product of the elements of A be 36 and p respectively and the sum and the product of the elements of B be 36 and q respectively. Let d and D be the common differences of AP's in A and B respectively such that $D=d+3, d \gt 0$. If $\frac{p+q}{p-q}=\frac{19}{5}$, then $p-q$ is equal to
  1. $600$
  2. $450$
  3. $630$
  4. $540$

Solution

$\begin{array}{lc}\text { Let } A(a-d, a, a+d) & B(b-D, b, b+D) \\ \quad a=12 & b=12 \\ p=12\left(144-d^2\right) & \\ q=12\left(144-D^2\right) & \\ \frac{p+q}{p-q}=\frac{19}{5} & \end{array}$
$\begin{aligned} & \frac{p}{q}=\frac{24}{14}=\frac{12}{7} \\ & \frac{144-d^2}{144-\left(d^2+6 d+9\right)}=\frac{12}{7} \\ & 1008-7 d^2=-12 d^2-72 d+1620 \\ & 5 d^2+72 d-612=0 \\ & d=6 \\ & D=9 \\ & p-q=12\left(D^2-d^3\right) \\ & =12(81-36) \\ & =12(45) \\ & =540 \\ & \text { option }(4)\end{aligned}$ *

Asked in: JEE Main 2025 (04 Apr Shift 2)

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