someone can mow his lawn in 48 minutes. if his daughter helps, they can do it in 40 minutes, how long would it take for his daughter to mow the lawn by herself?

Answer 1

someone's rate = 1/48
daughter's rate = 1/x
combined rate = 1/48 + 1/x
= (x + 48)/(48x)

so 1/[(x + 48)/(48x) ] = 40
cross-multiply

40x + 1920 = 48x
8x = 1920
x = 240

slow daughter, testing answer

someone's rate = 1/48
daughter's rate = 1/240
combined rate = 1/48 + 1/240 = 1/40

time at combined rate = 1/(1/40) = 40

it will take the daughter 240 minutes to do the job by herself.

Answer 2

The total resistance of two circuits in parallel is 15 ohms and one circuit has five times the resistance of the other, find the resistance of each circuit. Use 1/R=1/R1+1/R2. R1 and R2 are two individual resistances.

a)Find the smaller resistance
b)Find the larger resistance