Question 21 • Mathematics III
The inverse of 5 is 5⁻¹. When multiplying powers with the same base, add the exponents: 5⁻¹ × 5⁻³ = 5⁻⁴. A negative exponent means take the reciprocal, so 5⁻⁴ = 1/5⁴ = 1/625. The correct choice is 1 over 625.
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