What is the sum of the first 9 positive multiples of 5?
A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.
Solution
Since 1+2+3+4+5+6+7+8+9=45 then 5+10+15+⋯+40+45=5(1+2+3+⋯+8+9)=5(45)=225
Want a route through all this instead of an archive? The track
puts 2,604 problems in a working order, from Junior Challenge level to the IMO shortlist.
Source: Omni-MATH,
licensed Apache-2.0.
Statement reproduced verbatim; metadata (topic, difficulty) added by this project.