Answer:
10.25
Explanation:
Define the variable
Let x be the unknown number.
Therefore:
![\begin{aligned}& \textsf{Four times a number}: \quad & 4x\\& \textsf{Twenty less than four times a number}: \quad & 4x-20\\& \textsf{Twenty less than four times a number is twenty one}: \quad & 4x-20=21\end{aligned}](https://img.qammunity.org/2023/formulas/mathematics/college/j8n64kivokdbgf89auqj0tb27dm2e83dcq.png)
To find the number, solve the found equation for x:
![\begin{aligned}\implies 4x-20&=21\\4x-20+20&=21+20\\4x&=41\\(4x)/(4)&=(41)/(4)\\x&=10.25\end{aligned}](https://img.qammunity.org/2023/formulas/mathematics/college/63j5zocdk93fw8kzwvpb91pm8zq7602the.png)
Therefore, the unknown number is 10.25.
As an improper fraction, this is ⁴¹/₄.
As a mixed number, this is 10 ¹/₄.