# Do you know its Property-3

Algebra Level 4

$$a_n$$ is the nth term of an increasing arithmetic progression. If $\sum_{r=1}^{4000}\frac{1}{a_r a_{r+1}}=10$ and $$a_{2001}=25$$, what is the value of $$|a_1-a_{4001}|$$?

You can try more such problems of the set Do you know its property ?

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