To convert numbers like 100 to 1.0 and 99 to 1.1 in Excel, a linear function can be used, expressed as y = ax + b. For the specific conversions requested, the equations yield a = -0.1 and b = 11, resulting in the formula y = -0.1x + 11. However, this formula does not convert 25 to 2.5; it gives y = 8.5 instead. To achieve the desired transformation for all specified values, a quadratic function would be necessary, requiring a more complex set of equations to solve for coefficients a, b, and c. Rethinking the approach may be beneficial to clarify the intended conversions.