At school it is necessary to paint 180 doors. One painter will paint all doors in 15 days, and another - in 10 days. For how many days will they paint all doors, working together?

180:15=12 doors a day are painted by 1 painter of 180:10=18 doors a day the 2nd painter of 12+18=30 doors paints pass paint 2 painters together 180:30=6 days 2 painters together will paint all doors
Answer add