Q.A trader receives three bills — ₹2,000 due on the base date itself, ₹3,000 due 40 days after the base date, and ₹5,000 due 100 days after the base date. Find the average due date, measured in days after the base date.

Compute the amount-weighted average of the number of days each bill falls due after the base date.

$\sum a_it_i = 2{,}000(0)+3{,}000(40)+5{,}000(100)=0+1{,}20{,}000+5{,}00{,}000=6{,}20{,}000$. …

Here the three bills are $a_1=₹2{,}000$ at $t_1=0$ days, $a_2=₹3{,}000$ at $t_2=40$ days, and $a_3=₹5{,}000$ at $t_3=100$ days, all measured from the chosen base date.

Step 1 — Compute each product $a_i t_i$.

Step 2 — Sum the products and the amounts.

Step 3 — Divide to get the average day-count. …

Computing a plain (unweighted) average of the three day-counts — $(0+40+100)/3\approx46.67$ days — ignores that the bills are of very different sizes; the correct average due date must be weighted by each bill's …