Voltage Divider producing unexpected voltage
Your math only holds true if there is NO load between the 2 resistors. Even a DVM with a 10M ohm input will cause a slight drop in the value, but if your using 5% tolerance resistors you could have a +/-10% error in the actual voltage. To get close to 4.500vdc you need an accurate 9.00vdc source, and use 1% or even .1% resistors to increase accuracy. Now you should have 4.50vdc at the test point, minus the 10M load of the DVM, which is about .05%, giving you a reading of 4.497vdc under ideal conditions. Leave out the LED as it is shorting out your divider. Your meter reading of 1.83 volts is actually the voltage the LED is clamping at to work properly. The DVM is a better test method in this case.NOTE: 4.7K 10% and 5% resistors go back about 40 years or more. To get 1% or 0.1% tolerance resistors you may need to use their common values, such as 4.99K.