Small long division

Logic Level 1

Below is a long division with some digits hidden. Which of the following digits could represent one of the empty boxes?

5 6 7 8

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10 solutions

Marta Reece
Jul 2, 2017

There are two possibilities.

13 ÷ 3 = 4 13\div3=4 with remainder 1 or 33 ÷ 8 = 4 33\div8=4 with remainder 1.

Only the second version contains a number on the list, namely 8 \boxed8

Moderator note:

This particular long division layout is used in multiple countries including South Korea, Japan, and the United States.

Most countries follow a similar pattern (the most common difference is having the quotient be written to the right rather than above the problem), but there are a few major variations; two samples shown below.

73/18=4 remainder 1, 18x4=72, 7 is a correct answer also.

Dave Mckendrick - 3 years, 11 months ago

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The divisor has only one digit, so it cannot be equal to 18.

Pi Han Goh - 3 years, 11 months ago

In Portugal we don't use that way to solve

Tito Fidalgo - 3 years, 9 months ago

I have never seen this kind of notation for a division. I don't think it's used in Germany and Austria?

Jan Fischer - 3 years, 8 months ago

I'm portuguese and I don't use that way.

A Former Brilliant Member - 2 years, 5 months ago

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Care to elaborate? Do you have a different way to write out your long division?

Pi Han Goh - 2 years, 5 months ago

I meant that in my country (Portugal), we actually use what is described above as Argentina's way.

A Former Brilliant Member - 2 years, 5 months ago

excuse me ? i haven't seen this problem before , i mean this "long division" , so i don't understand how this division worked . could you please give me an explanation ? thank you !

The Linh Nguyen - 3 years, 11 months ago

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Long division written this way is a bizarre way American kids are taught to do division, or used to be. I didn't run into it myself until I was an adult, and for solving this problem I had to look it up on Google to figure which number goes there, as it it definitely counter-intuitive. I think the problem should carry an explanation of the system, since people around the world cannot be expected to know it.

Marta Reece - 3 years, 11 months ago

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I agree. Maths should be universal language. I had the same problem. But was too lazy (and angry I guess) to get through google to find information.

Ivan Constantineau - 3 years, 11 months ago

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@Ivan Constantineau Really? I'm pretty sure everyone learned what long divisions before the age of 10.

Regardless, how do you think I could clarify what "long division" is?

Pi Han Goh - 3 years, 11 months ago

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@Pi Han Goh I learned a long division as a small child. I learned it using a totally different notation, however.

Marta Reece - 3 years, 11 months ago

53/13=4 with remainder of 1 also works! So 5 is also a correct answer.

Shirley Jensen - 3 years, 11 months ago

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True, but 13 does not fit into a single square provided, as it has two digits, so it cannot be an answer. In other words you can't fill the entire long division outline correctly using this option.

Marta Reece - 3 years, 11 months ago

The number (we'll call y) must be such that y × 4 + 1 = number ending with 3 in the ones place. The possible numbers that work are 3 and 8. The number given is 8, thus, the only number on the list that works is 8.

8 × 4 + 1 = 33

Wesley Zumino
Jul 11, 2017

A systematic algebraic approach: Let k k be the divisor, m m be the 10's place digit of the dividend, and n n the 10's place digit of the number below the dividend. k , m , and n k, m, \text{ and } n are all digits in { 1 , 2 , , 9 } \{1, 2, \ldots, 9\} . Then from the structure of the division problem:

( 1 ) 10 m + 3 ( 10 n + 2 ) = 1 10 m 10 n = 0 m = n (1) \; 10m + 3 - (10n+2) = 1 \; \Rightarrow \; 10m - 10n = 0 \; \Rightarrow \; \underline{m = n}

( 2 ) 10 m + 3 = 4 k + 1 5 m + 1 = 2 k m (2) \; 10 m + 3 = 4 k + 1 \; \Rightarrow \; 5 m + 1 = 2 k \; \Rightarrow \; m must be odd and k = 1 2 ( 5 m + 1 ) \underline{k = \frac{1}{2}(5 m + 1)} for m m odd.

So, trying m { 1 , 3 , 5 , 7 , 9 } m \in \{1, 3, 5, 7, 9\} gives only two possible single-digit ( m , k ) (m,k) solutions: ( 1 , 3 ) (1,3) and ( 3 , 8 ) (3,8) . Only 8 \boxed{8} is a solution option.

Akshay Gupta
Jul 15, 2017

Only thing we have to focus is that 4 and 2

We have to find a sure number that is in the options and can fill any of the boxes, so the only thing we can calculate is a multiple of 4 whose one's digit 2

Only possibilities : 4 x 3 = 12

4 x 8 = 32

Only 8 is available in options, hence answer is 8

Arianna Colella
Jul 13, 2017

It is possible to solve this problem knowing only the two and the four. By following the long division procedure, we know that 4 times a single digit number must give a double digit number with two as its last digit. The second single-digit factor must be one of the options provided, so we have either: 4 x 5= 20, 4 x 6= 24, 4 x 7= 28, and 4 x 8= 32. Since 8 is the only factor that gives a product ending with 2, it must be the answer.

Katy B
Jul 12, 2017

The first omitted digit, the divisor, has to be larger than the omitted number of the dividend, since the quotient is one digit. Also, since there is only a remainder of 1, the second two omitted numbers have to equal each other. There is only one number on the list which meets these requirements - 8, since 33 ÷ 8= 4, with a remainder of 1.

Jennifer Thompson
Jul 12, 2017

The two digit multiples of 4 with two ones are 12 and 32. You cannot go past 32 because then the divisor will not be a single digit anymore. Since 3 and 4 do not appear as choices, the answer must be 33/8.

Mohammad Khaza
Jul 11, 2017

it should be,

4x+1=..3

or, 4x+1=33.............[without 3, no numbers work here]

or. 4x= 32

or,x=8

Paola Ramírez
Jul 10, 2017

Let be n n the divisor the division, n × 4 n\times4 it must finish in 2 2 . \therefore 8 × 4 = 32 8\times4=32 finish in 2 2

good attempt, but your solution is incomplete. 3x4 = 12 <<< it finish in "2" as well.

Pi Han Goh - 3 years, 11 months ago
Benjamin Byers
Jul 9, 2017

Of the answer choices, only one of them (8) offers a product of 4 with 2 as its first digit.

Yes, 8 is the right answer. Can you show us why this is indeed the correct answer?

Pi Han Goh - 3 years, 11 months ago

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