How many hours are required to build 210 snowballs in the following case?
Justin is making snowballs to build a fort on the winter break. He can build 15 snowballs/hour but two snowballs melt every 15 minutes. How long will it take him to build 210 snowballs.
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Justin builds 15 snowballs in an hour and 2 snowballs melt every 15 minutes.
So in an hour he makes 15 snowballs of which 2*4 = 8 melt leaving him with 7.
As he needs to build 210 snowballs, it will require 210/7 = 30 hours.
The total time required to build 210 balls is 30 hours.
Since 2 snowballs are melting every 15 minutes, we'll compute how many snowballs does Justin really make in an hour.
Since 1 hour = 60 minutes = 4*15 minutes, the number of snowballs melt in an hour is = 4*2 = 8 melted snowballs.
We'll subtract 8 snowballs from the total numbers,15, of snowballs made in an hour.
The number of snowballs from an hour = 15 - 8 = 7snowballs/hour
Now, we'll apply the rule of three:
7 snowballs..................................1 hour
210 snowballs...............................x hours
We'll cross multiply:
x = 210/7
x = 30 hours for making 210 snowballs.
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