First we list the multiples of each number. multiples of 5 are 10,15,20,25,30,35,40,... multiples of 6 are 12,18,24,30,36,42,48,... multiples of 15 are 30,45,60,75,90,... now, when you look at the list of multiples, you can see that 30 is the smallest number that appears in each list. therefore, the least common multiple of...... 5,6 and 15 is 30.
For example: Price of ice cream in june was 10$ and amount of ice cream sold is 100. Store earned 10$*100=1000$ Price of ice cream in july has been decreased by 10%. Price of ice cream is now 9$. The amoun of ice cream sold in july increased by 24% compering to june. So amount of sold ice cream in july is 124. Store earned 9$*124=1116$.