cut the log

Geometry Level 1

A 100-meter long log is to be cut into smaller pieces. How many times would a cutter cut the log so that each piece is 2.5 meters long?


The answer is 39.

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Ryan Redz by Ryan Redz , 39, Philippines

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8 solutions

Ryan Redz
Jul 20, 2014

100 meters divided by 2.5 is 40, so there will be 40 pieces of 2.5-m log. however we need only 39 cuts to accomplish that because both ends of the log were already cut.

18 Helpful 0 Interesting 0 Brilliant 0 Confused

If we have to cut a log into two pices then we have to cut it only one time, for three it is two and for four it is three times. So it gives a relation of n-1 where n is the no of logs needed. Now, since the length of the log is 100 m and pieces should be of length 2.5m gives 2.5 * 40=100 So 40 pieces is to be cut. So from the above explaination we can say that No of cutting operations =40-1=39

Shubhanshu Mishra - 6 years, 10 months ago

39 because, we are not going to cut the lasr piece. in fact hypothetically answer is 40.

Meet Patel - 6 years, 10 months ago

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opps sorry spelling mistake - *last

Meet Patel - 6 years, 10 months ago

very good question

Achal Goyal - 6 years, 8 months ago

We can just divide 100 by 2.5 then add 1 for when we cut it once it results to.

Kim Diate - 6 years, 10 months ago

1 cut =2 pieces, Therefore, n cutes= n+1 pieces, n+1=40 n=39

2 Helpful 0 Interesting 0 Brilliant 0 Confused

I knew it was not 40, but did the same as you and verified my conjecture inductively by making a chart: 2pieces = 1cut, 3pieces=2cuts, ... 40pieces=39cuts.

Gary Brown - 6 years, 8 months ago

Did the same

Sonal Singh - 5 years, 9 months ago
Mazahir Hussain
Sep 4, 2014

the cutter should have to cut the long log 39 times , because the last piece will be autonmatically 2.5 meter left.

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Megha Pardhi
Jul 22, 2014

100/2.5=40. for 40 pieces we need 39 cuts.

1 Helpful 0 Interesting 0 Brilliant 0 Confused

The number of cuts is 100 2.5 − 1 = \dfrac{100}{2.5} -1= 39 \large \color{#D61F06}\boxed{39} .

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Windy Wings
Dec 21, 2014

Cutting the log into 2 pieces needs 1 time, 3 pieces needs 2 times... and if each piece is 2.5 meters long, the log would be cut into 40 pieces. Hence, the cutter would cut 39 times.

0 Helpful 0 Interesting 0 Brilliant 0 Confused

first u will divide the 100 by 2.5 it gives 40 but u have a log so u have to consider a piece so when u will minus it from total pieces like 40-1=39 u will get answer

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Shiv Kaundilya
Jul 22, 2014

39, at last cut it left with 2 38 plus 2 from last total 40

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