Question

Estimate how many times larger 4 x 1015 is than 8 x 109 in the form of a single digit times an integer power of 10.

Answer 1

(4×10¹⁵)/(0.8×10¹⁰) = 5×10¹⁵⁻¹⁰ = 5×10⁵

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I find it convenient to scale the numbers prior to division so the result comes out in the range I want.