Class 11

Math

Co-ordinate Geometry

Straight Lines

Find the sum of all four digit numbers that can be formed using the digits $1,3,5,7,9$.

So for digit $k$ sum of it's influence in all numbers $=(k×10_{3}+k×10_{2}+k×10+k)4×3×2$

$=k×(1111)4×3×2$

So for $1,3,5,7,9$

$=(1111)×4×3×2(1+3+5+7+9)$

$=666600$