(emergency) maths equation form 1

Question

mary and ann will finish a piece of work in 3 days.Mary alone will finish it in 5days.How many days will Ann need to finish the work by herself?

please in detail

thank you

Answer 1

最愛解答

Let the speed of mary is x piece per day, the speed of ann is y piece per day. Total speed is (x+y) piece per day

Then we have

3(x+y)=1 (total work 1 piece)

On the other hand

Mary alone will finish it in 5days. So

5x=1

Then

3(x+y)=5x

3y=2x

y=(2/3)x

From 5x=1, x=0.2. y is 2/15

The speed of ann is 2/15 piece per day

The days Ann need to finish the work by herself

=1/(2/15)

=15/2

=7.5 days