If it takes a hrs for x to repair 1 machine and b hrs for y to repair 1 machine then how many hrs will they take to repair 750 machines if they work together? Choose the most appropriate option:
A) 750 × ab/(a+b)
B) 750 (a+b)/ab
C) 750 ab
D) 750/(a+b)
E) None of these
Explanation:   x repair machine in a hrs he work 1/a for 1 hr   y repairs machine in b hrs he works 1/b for 1 hr   (x+y) work per 1 hr = 1/a+1/b= (a+b)/ab   time = ab/(a+b)   for 750 machines time = 750 × ab/(a+b)   750 × ab/(a+b)nswer: Option 750 × ab/(a+b)
<result>A</result>
If it takes a hrs for x to repair 1 machine and b hrs for y to repair 1 machine then how many hrs will they take to repair 750 machines if they work together?