Question 277229
1/12=1/x+1/(x+10)
1/12=(x+10+x)/x(x+10)
1/12=(2x+10)/(x^2+10x)
12(2x+10)=x^2+10x
24x+120=x^2+10x
x^2+10x-24x-120=0
x^2-14x-120=0
(x-20)(x+6)=9
x-20=0
x=20 hours for the experienced bricklayer.
Proof:
1/12=1/20+1/30
1/12=(30+20)/20*30
1/12=50/600
12*50=600
600=600