SOLUTION: On 1 Jan 2014 a bird sanctuary is home to 25 birds. During Jan 2014, 3 more birds are brought into the sanctuary. During each subsequent month, 2 more birds are brought into the sa

Question 1043879: On 1 Jan 2014 a bird sanctuary is home to 25 birds. During Jan 2014, 3 more birds are brought into the sanctuary. During each subsequent month, 2 more birds are brought into the sanctuary than were brought in during the previous month. Assuming that no birds die or leave the sanctuary, work out how many birds are in the sanctuary on 31 Dec 2014.
This is what I understand......
at the end of Jan there are 28 birds. During Feb, 2 more than the previous month are brought in i.e. 28(jan total) + 3 (the total brought in during Jan)+2 (the two more) i.e. 33 birds. During March 33 + 5 (from Feb) +2 = 40 During April = 40 + 7 +2 etc etc
I can happily check my total of birds but unsure how to write the formula/equation. help!!!! thanks
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
There are 28 after the end of January with 11 months to go.
One way to write 28+5+7+9 is 25+ [sum from 1 to 12 (2n+1)]
You have to write out what you want and then work a little with the numbers. increasing by 2 makes for a 2n and the odd number is taken care of with. Then you have to carefully check and see what you have. This will be 25+(3+5+7+...+25). The parentheses are to make sure that everything inside is added to the original 25.
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