I need some help with my math homework....pleease please please ?

Question

an office has two machines that can pout postage on batches of envelopes. Machine A can put postage on a batch of envelopes in 20 minutes and Machine B can put postage on a batch of envelopes in 12 minutes. How long in minutes would it take the two machines working together to put postage on a batch of envelopes

please show me how to do and the answer of the question

please

Answer 1

It's multiples.Look:

20 40 60 80 100 120

12 24 36 48 60 72 84 96 108 120

When is the first time 12 & 20 have the same numbers?

Answer:60 min. or 1 hr.

So machine A and B will work together to postage envelopes in 60 min.

Sorry very much if I'm wrong,but this is what I would write.

Answer 2

If machine A can make one batch in 20 minutes, then it can make 3 batches in 60 minutes.  

If Machine B makes one batch in 12 minutes, then it can make 5 batches in 60 minutes.

Therefore, both machines together can make 8 batches in 60 minutes (8/60).  So the question becomes if both machines can make 8 batches total in 60 minutes, how long for both of them to make one batch.  THis question is answered by the following equation:

8/60 = 1/t (where t is time)

You cross multiply and get 8t=60

t=7.5

therefore, both machines working together will make a batch in 7.5 minutes.

Answer 3

I got the answer 7.5 minutes.

95% sure of accuracy.

Here's how:

Use the basic principle Rate x Time = Distance.

Machine A:

Rate x 20 min = 1 batch

Rate = 1/20  batch/min

Machine B:

Rate x 12 min = 1 batch

Rate = 1/12  batch/min

Machine A + Machine B:

(1/20 + 1/12) batch/min x Time = 1 batch

Time = 1 batch/(1/20 + 1/12) batch/min

When you simplify the fraction, you get 7.5.

Hope this helps!