1. (10101)₂ = (      ?      )₁₀

Solution:
`(10101)_2 = (underline{" "})_10`


`10101`

` = 1 × 2^4 + 0 × 2^3 + 1 × 2^2 + 0 × 2^1 + 1 × 2^0`

`= 1 × 16 + 0 × 8 + 1 × 4 + 0 × 2 + 1 × 1`

`= 21`


`:. (10101)_2 = (underline{21})_10`

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2. (110101001)₂ = (      ?      )₁₀

Solution:
`(110101001)_2 = (underline{" "})_10`


`110101001`

` = 1 × 2^8 + 1 × 2^7 + 0 × 2^6 + 1 × 2^5 + 0 × 2^4 + 1 × 2^3 + 0 × 2^2 + 0 × 2^1 + 1 × 2^0`

`= 1 × 256 + 1 × 128 + 0 × 64 + 1 × 32 + 0 × 16 + 1 × 8 + 0 × 4 + 0 × 2 + 1 × 1`

`= 425`


`:. (110101001)_2 = (underline{425})_10`

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