Answer:
Exact: 3,999,500,000
Estimate: 4,000,000,000
Explanation:
(4)(10) = 40
(4 x 10)9 = 4,000,000,000
Notice that there are 9 zeros
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(5)(10) = 50
(5 x 10)5 = 500,000
Notice that there are 5 zeros
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4,000,000,000 - 50,000 = 3,999,500,000