What is result of 6.25 to power 3/5

Alan's answer is an approximation.

Just use the calculator on the home page here.

$${{\mathtt{6.25}}}^{\left({\frac{{\mathtt{3}}}{{\mathtt{5}}}}\right)} = {\mathtt{3.002\: \!811\: \!084\: \!953\: \!578\: \!1}}$$

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