Question 200529
{{{1/(R[t])=1/12+1/15+1/5}}} Start with the given equation.



{{{60*cross(R[t])(1/cross(R[t]))=cross(60)^5*R[t](1/cross(12))+cross(60)^4*R[t](1/cross(15))+cross(60)^12*R[t](1/cross(5))}}} Multiply EVERY term by the LCD {{{60R[t]}}} to clear out the fractions.



{{{60=5R[t]+4R[t]+12R[t]}}} Multiply and simplify



{{{60=21R[t]}}} Combine like terms.



{{{60/21=R[t]}}} Divide both sides by 21 to isolate {{{R[t]}}}.



{{{R[t]=60/21}}} Rearrange the equation.



{{{R[t]=20/7}}} Reduce



{{{R[t]=2.8571}}} Approximate the right side



So the total resistance is approximately 2.8571 ohms (assuming that's the unit you're working with).