Question 22029
I THINK I ANSWERED THIS  QUESTION GIVING EXAMPLES.IF YOU HAVE NOT UNDERSTOOD IT,LET ME SOLVE..THE KEY IN THESE PROBLEMS IS TO FIND WORK DONE PER UNIT TIME FIRST FROM GIVEN DATA,COMBINE THEM AS REQUIRED AND THEN FIND THE TIME REQUIRED TO DO THE FULL JOB(THAT IS REVERSE THE FIRST STEP)WE HAVE....
SALLY CAN PAINT 1 HOUSE IN 4 HRS..SO IN 1 HR SHE CAN DO 1/4 HOUSE
JOHN CAN PAINT 1 HOUSE IN 6 HRS...SO IN 1 HR HE CAN PAINT 1/6 HOUSE...
SO TOGETHER THEY CAN PAINT 1/4 +1/6 HOUSE IN 1 HR =(3+2)/12 HOUSE IN 1 HR.=5/12 HOUSE IN 1 HOUR....
SO FULL HOUSE THEY CAN PAINT IN 1/(5/12)=12/5=2.4 HRS.=2HRS AND 0.4*60=24 MTS.OR 2HRS 24 MTS. TIME.