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Algebra Difficulty 1.7 Junior Find the answer
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
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