2resistors 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

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

Let Rp denote parallel combination.

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±1.8ohm.