Series and parallel resistors
Both formulas, on one screen, with the half of the answer a formula does not give you: whether the combination beats the nearest single part already in the drawer.
3.2 kΩ
1 kΩ + 2.2 kΩ = 3.2 kΩ
R1
R2
3.2 kΩ is above the 2.2 kΩ you started from, and a series chain is never below its largest part. The nearest stock part, 3.3 kΩ, is 3.1% off, which a ±5% resistor could be anyway.