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by helpmeplease on September 23rd, 2007

helpmeplease

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A wall is 10 feet tall. an insect crawls up the wall 9 inches each day but slips down 2 inches each night. on what day will the insect reach the top of the wall.

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  • by Rince on September 23rd, 2007

    Rince

    First convert feet to inches, 10 X 12 = 120. Then the insect travels at 9 - 2 = 7 inches per day. You can do the rest :-) ( simple division )

    Comments

    • Perfect explanation.

      Jodie44

      by Jodie44 on September 23rd, 2007

    • But there's a catch -- on the last day it goes 9 inches and gets out without slipping back down 2 inches.

      xprofessor

      by xprofessor on September 23rd, 2007

    • Yeah but if you devide by the 7 ( in any 24 hour period ) The answer comes out the same and the little insect ( bless him ) clears the wall on the **th day, with inches to spare :-)

      Rince

      by Rince on September 23rd, 2007

    • No, the bug actually gets out a day earlier than the answer you get by figuring 7 inches a day.

      xprofessor

      by xprofessor on September 23rd, 2007

    • Does he ? Hmmm... I'll have to work that one out again, cheers for the comment, I'll check it :-)

      Rince

      by Rince on September 23rd, 2007

    • After 16 days, he has done 112 inches, On the 17th day he does 9 and clears the wall ( total 121 ), My answer 120/7 = 17.14, ie 17th day, same answer :-) Day 17. Have I gone wrong somewhere ?

      Rince

      by Rince on September 23rd, 2007

    • How long does the average insect live, anyway?

      Jodie44

      by Jodie44 on September 23rd, 2007

    • 17 days too long by the look of it :-p

      Rince

      by Rince on September 23rd, 2007

    • I agree that the top is reached on the 17th day. The naive answer is to take an average of 7 inches per day, compute a requirement of 17.14 days, then wrongly assume the progess is insufficient after 17 days, making the answer 18 days, which is wrong.

      xprofessor

      by xprofessor on September 23rd, 2007

    • At least we agree on the answer, and gave the person who asked the question something to think about :-)

      Rince

      by Rince on September 23rd, 2007

    • I gave you max points :)

      xprofessor

      by xprofessor on September 23rd, 2007

    • The question asks 'on what day', so it will be on the 18th. Incompleted after 17 days and completed before the end of the 18th day.

      Farino

      by Farino on September 23rd, 2007

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