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? answer asap.

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


The second can also print in 7½ seconds

So the rate of printing is




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

Then their combined rate


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

That is



So we multiply through by the LCM which is


This implies that






Hence it will take them