Question

a can do a piece of work in 20 days which b alone can do it in 12 days b worked at it for 9 days a can finish the remaining work in

Answer 1

a can do the work in 20 days
b can do in 12 days
b worked it for 9 days
this is a inverse proportion
X1/y1=x2/y2
x1=20
y1=12
x2=9
20/12=9/y2
y2=15

hope you understand
thank you

Answer 2

the answer is 15 days because 20/12=X/9
20×9=12x
180=12x
180/12=X
15=X

so a can do the work in 15 days