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What is the value of 21×3+23×5+25×7+⋯+245×47\frac{2}{1 \times 3} + \frac{2}{3 \times 5} + \frac{2}{5 \times 7} + \dots + \frac{2}{45 \times 47}1×
Question

What is the value of 21×3+23×5+25×7++245×47\frac{2}{1 \times 3} + \frac{2}{3 \times 5} + \frac{2}{5 \times 7} + \dots + \frac{2}{45 \times 47} ?​

A.

46/47

B.

47/48

C.

49/50

D.

45/46

Correct option is A

Solution:

21×3+23×5+25×7++245×47\frac{2}{1 \times 3} + \frac{2}{3 \times 5} + \frac{2}{5 \times 7} + \dots + \frac{2}{45 \times 47} 

2n×(n+2)=22(1n1n+2)\frac{2}{n \times (n+2)} = \frac{2}{2} \left( \frac{1}{n} - \frac{1}{n+2} \right) 

(1113)+(1315)++(145147)\left( \frac{1}{1} - \frac{1}{3} \right) + \left( \frac{1}{3} - \frac{1}{5} \right) + \dots + \left( \frac{1}{45} - \frac{1}{47} \right) 

1147=46471 - \frac{1}{47} = \frac{46}{47}

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