Not understanding why my resistor R4 for the circuit schematic is reading 35k ohms on a multimeter when its meant to be 47k ohms?
Not understanding why the 47k ohm resistor (R4) reads 35k ohm on the
  multimeter


The LM386 input impedance is \$\text{50k}\Omega\$. What you're really measuring is the 47k, in parallel with 24k and 50k in series. This is the equivalent circuit.







simulate this circuit &ndash; Schematic created using CircuitLab


  How do i calculate what this resistor value will be due to the
  difference? As in i find what value i want, in this case i needed 47k
  ohm for the specified application but due to this resistor value
  difference, how am i meant to see what 47k will actually be. As in
  will i need to use a 56k or something to get the 47k due to the
  difference? Hence what formula am i meant to use to find what value
  this resistor will actually be when in theory its meant to be 47k
  ohms?


It looks like you're just trying to attenuate and filter a square wave. The datasheet only gives typical values for input impedance, so you can't rely on it being tightly controlled. You're going to have to decide how much variance you can tolerate. The easiest thing to do is keep your circuit as designed, and put a cheap rail-rail op amp in as a buffer.