Try this TOMATO problem from I.S.I. B.Stat Entrance Objective Problem based on Series and Integers.
The value of \(\sum ij\), where the summation is over all i and j such that \(1 \leq i \lt j \leq 10\)
Series
Integers
Inequality
Answer: 1320
B.Stat Objective Question 81
Challenges and Thrills of Pre-College Mathematics by University Press
required sum=1(2+3+4+....+10)+2(3+4+....+10)+3(4+5+....+10)+4(5+6+....+10)+5(6+7+....+10)+6(7+8+..+10)+7(8+9+10)+8(9+10)+9(10)
=54+104+147+180+200+204+189+152+90
=1320
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