Let the total work be 40 unit [LCM of 8 & 10] Efficiency of A=40∕8=5 Efficiency of B=40∕10=4 ⇒ Combined efficiency of (A+B)=5+4=9 unit ⇒ Time taken by (A+B) when working together =40∕9 Now, According to the question ⇒ Time taken by C to complete the work =40∕9 ⇒ Efficiency of C=40÷(40∕9)=9 unit Now, We have to find the time taken by B and C ⇒ Combined efficiency of (B+C)=4+9=13 unit ⇒ Time taken by (B+C) to complete the work =40∕13 ⇒3
1
13
hours. ∴ Time to complete the work by (B+C) together is 3