Question 1036106
I'm assuming the .06 is supposed to be 0.6



{{{1/f =0.6*(1/(r[1])+1/(r[2]))}}}



{{{1/f = 0.6*(1/4+1/6)}}}



{{{1/f = 0.6*(3/12+2/12)}}}



{{{1/f = 0.6*(5/12)}}}



{{{1/f = (6/10)*(5/12)}}}



{{{1/f = (6*5)/(10*12)}}}



{{{1/f = 30/120}}}



{{{1/f = 1/4}}}



{{{f = 4}}}



The final answer is D) 4