Question

One printing press can print 5,000 advertising cards in 12 seconds. Another printing press can print the same number of cards in 7 1/2 seconds. If both presses are used together to print the 5,000 cards, how many seconds will it take them?

Please answer ASAP.

Answer 1

I think it is the answer is 4.62

Tell me if its right

Answer 2

We first of all find the rate at which each of them print,

The first can print 5,000 cards in 12 seconds
So the rate of printing is

`= (1)/(12)`

The second can also print in 7½ seconds

So the rate of printing is

`= (1)/(7 (1)/(2) )`

`= (1)/( (15)/(2) )`

`= (2)/(15)`


Now let the time taken by both to complete be t.

Then their combined rate

`= (1)/(t)`


So adding their individual rate should give us the combined rate.

That is


`(1)/(12) + (2)/(15) = (1)/(t)`

So we multiply through by the LCM which is

`60t`


This implies that


`(60t)/(12) + 60t * (2)/(15) = ( 60t )/(t)`

`5t + 8t = 60`

`13t = 60`

`t = (60)/(13)`

Hence it will take them

`t = 4 (8)/(13) \: seconds`