Two resistors are to be combined to form an equivalent resis

Two resistors are to be combined to form an equivalent resistance of 3000 ohm . The resistors are taken from available stock on hand as acquired over the years. Readily available are two common resistors rated at 500 ohm (+ and - )50 and two common resistors rated at 4000 ohm (+ and -) 5%. What combination of resistors (series or parallel) would provide the smaller uncertainty in an equivalent 1000 ohm resistance?

Solution

combining two 4000 ohm resistors in parallel will result in lesser uncertainty

1/Req = 1/4000 + 1/4000

= 2/4000 +- 5%

Req = 2000 +- 2.5%

for the case of joining the 500 ohm resistors in series we get greater uncertainty than this