Change in parallel resistance when one resistor increases and one decreases

[eleventhxhour]

When two resistors, $$s$$ and $$t$$, are connected in parallel, their combined resistance, $$R$$, is given by $$\frac{1}{R}$$ = $$\frac{1}{s}$$ + $$\frac{1}{t}$$

If $$s$$ is increased by 1 unit and $$t$$ is decreased by 1 unit, what is the change in $$R$$?(I'm not really sure how to do this...help would be appreciated! Thanks.)

 

[MarkFL]

I would first solve for $R$ and call this $R_i$, or the initial resistance. The substitute $s+1$ for $s$ and $t-1$ for $t$ in that expression and call that $R_f$, or the final resistance. Then compute the change in the resistance by:

$$\Delta R=R_f-R_i$$