# SOLUTION: Printing press A can print an order in 7hours. If printing press B is used along with press A, the job can be completed in 5hr. How long would it take printing press B to print the

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 Question 81772: Printing press A can print an order in 7hours. If printing press B is used along with press A, the job can be completed in 5hr. How long would it take printing press B to print the job by itself?Found 2 solutions by Edwin McCravy, dolly:Answer by Edwin McCravy(8909)   (Show Source): You can put this solution on YOUR website!``` Printing press A can print an order in 7hours. If printing press B is used along with press A, the job can be completed in 5hr. How long would it take printing press B to print the job by itself? Make the chart below. It is just like a D=RT chart except that D stands for "DEEDS" not "DISTANCE". In other words, D stands for the number of DEEDS or printing jobs done in each case. No of jobs Rate in jobs per hour Time in hours Press A only Press B Both presses ------------------------ We read: >>...press A can print an order in 7 hours...<< So that's 1 job in 7 hours. So we fill in 1 for the number of jobs which A alone does and 7 for the number of hours. No of jobs Rate in jobs per hour Time in hours Press A only 1 7 Press B Both presses ------------- Next we read: >>...If printing press B is used along with press A, the job can be completed in 5hr That's 1 job in 5 hours for both presses. So we fill in 1 for the number of jobs which both presses together do and 5 for the number of hours. No of jobs Rate in jobs per hour Time in hours Press A only 1 7 Press B Both presses 1 5 ----------------------- Now we read the question: >>...How long would it take printing press B to print the job by itself?...<< That asks how many hour would it that press B to do 1 job. So we let x be the number of hours press B would take to do 1 job. Se we efill in 1 nfor the number of jobs and x for the number of hours. No of jobs Rate in jobs per hour Time in hours Press A only 1 7 Press B 1 x Both presses 1 5 ---------------------- Now we fill in the rates by using the equivalent of DISTANCE RATE = ---------- TIME which is: NUMBER of JOBS RATE = ----------------- TIME No of jobs Rate in jobs per hour Time in hours Press A only 1 7 Press B 1 x Both presses 1 5 Now we use the formula: Rate of Press A + Rate of Press B = Rate of Both presses together + = Can you solve that? You have to multiply through by the LCD of 35x. If you can't solve it post again asking how. Answer: 17 hours. Edwin``` Answer by dolly(163)   (Show Source): You can put this solution on YOUR website!Time taken by press A = 7 hrs. So work done in 1 hr = 1/7 part Let the time taken by press B = x hrs So work done in 1 hr = 1/x part Together work done in 1 hr = 1/7 + 1/x = (x + 7)/7x Given they complete in 5 hrs. ==> they complete 1/5 part in 1 hr So (x + 7)/7x = 1/5 ==> 5(x+7) = 7x ==> 5x + 35 = 7x ==> 35 = 7x - 5x ==> 35 = 2x ==> 35/2 = x ==> 17.5 = x Thus B takes 17.5 hrs to complete all by itself