Answer:
c =4 4/9 minutes
Step-by-step explanation:
The formula is
1/a + 1/b = 1/c where a and b is the time for each working alone and c is the time working together
1/8 + 1/10 = 1/c
Multiply by 40c to clear the fractions ( 40c is the least common multiple)
40c(1/8 + 1/10 = 1/c)
5c + 4c = 40)
9c = 40
Divide by 9
9c/9 = 40/9
c =4 4/9 minutes