Twelve printing presses, all alike, can do a job in 3 hours. How many hours would it take 10 of these printing presses to do the same job?1)2.5 hours2)3.0 hours3)3.6 hours4)4.0 hours
If 12 presses do the job in 3hrs then each press is doing 1/12 of the job in 3hrs. Now, since you only have 10 presses, only 10/12 of the job is being done in 3hrs. How long for 10 presses to do 1 whole job? 10/12=5/6=.83 3/.83=x/1 .83x=3 x=3/.83 = 3.6hrs
use ratios. 12/3 = 10/x solve for x x=2.5
Let n be the amount of work that needs to be done; and let x be the amount of time it takes for 10 printing presses to accomplish n. We can write this as: x = n/10 We know that when n is divided among 12 printing presses, it can be accomplished in 3 hours. n/12 = 3 n = 36 Now we can substitute 36 for n. x = n/10 x = 36/10 x = 3.6 The answer is 3.6 hours.
use estimation. if you had 12 presses working and it took 3 hours, will it take longer or shorter if you get 2 fewer presses working on it? longer! so answer 1) is wrong, eliminate what you know is wrong! answer 2) is same as original, and you know it will take longer, so it is wrong. so answer must be 3) or 4). 12 press * 3 hours = 36 press hours of work. 36 press hours/10 presses= 3.6 hours checking: 12/10 * 3 = x. 36/10 = x 3.6 hours = x. checked.
