2 Resistors of resistance, R = (100 + - 3) Ohm, R2 = (200+-4) Ohm are connected in Parallel and Series.

Find the absolute error and % error in the measurement of equivalent resistance are in each combinations I. e Series and Parallel ... ?

According to what I've learnt, in any expression of multiplication or division, the percentage errors of each term are added up to find the equivalent percentage error. That is, if

y = ABC

y = ABC then % error in y = % error in A + % error in B + % error in C

For the above problem, let Rs denote series combination. Then Rs = 300±7 ohm.

Let Rp denote parallel combination.

∴ Rp = R1 R2 / R1 + R2 = R1 R2 / Rs

Ignoring errors, we get Rp = 200/3 = 66.67 ohm

% error in R1 = 3, % error in R2 = 2, % error in Rs = 7/3

Hence, % error in Rp = 3+2 + 7/3 = 22/3

So, error in Rp will be 22/3 % of 200/3, which is approximately 4.89.

Hence, I got Rp = 66.67±4.89 ohm.

However, the book used the formula described and proved here and arrived at the answer Rp = 66.67±1.8 ohm.