The reciprocal of 10b is...
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2b + 8
b + 4
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5b
1). Factor out the common term 2.
10b
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2(b + 4)
2). Divide 10/2 to get 5.
5b
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(b + 4)
3). Find the reciprocal by flipping the terms upside down.
b + 4
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5b