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susheelh
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Thanks naorba for the letting me know this is helpful! One Kudos to you for the appreciation! :)

naorba
susheelh
Hello!

I read somewhere that remembering the decimal equivalents of reciprocals of first 10 digits will help in solving fractions and percentages problems a bit faster. However, I was really struggling to remember the decimal equivalents and asked someone important - Google! :)

I found a very useful link that gives good tips on remembering the decimal equivalent of Reciprocals. The link follows - https://testbook.com/blog/remember-reci ... tcuts-pdf/

Here I summarize the tips to remember the reciprocals of 1 to 10. (The Tip of 7 is what I found most useful). I hope it helps you.

Reciprocal of 2

Simplest of the Lot. Reciprocal of \(2 = \frac{1}{2} = 0.5 = 50\)%

Reciprocal of 3

Reciprocal of \(3 = \frac{1}{3} = 0.3333 = 33.33\)%. Reciprocal of 3 contains all 3's.

Reciprocal of 4

Remember 4 parts of a 25 makes a hundred. So, Reciprocal of \(4 = \frac{1}{4} = 0.25 = 25\)%

Reciprocal of 5

If \(\frac{1}{2}\) is 0.5 then \(\frac{1}{5}\) is 0.2 = 20%! Obviously!

Reciprocal of 6

Reciprocal of \(6 = \frac{1}{6} = 0.1666 = 16.66\)%. You can memorize this or, you can half the reciprocal of 3.

Reciprocal of 7 and its multiples

Remember this sequence - 1 4 2 8 5 7

Tip to remember the sequence - 2 times 7 is 14, 2 times 14 is 28, 2 times 28 is 56. But you want to end it with a 7, so lets make it 57. Once you remember 1 4 2 8 5 7 - rest just forms a cycle.

\(\frac{1}{7} = 0.142857 = 14.2857\)% --> starts with the smallest number (1) in the sequence.

\(\frac{2}{7} = 0.285714 = 28.5714\)% --> same cycle but starts with the second smallest number (2) in the sequence

\(\frac{3}{7} = 0.428571 = 48.8571\)% --> same cycle but starts with the third smallest number (4) in the sequence

\(\frac{4}{7} = 0.571428 = 57.1428\)% --> same cycle but starts with the fourth smallest number (5) in the sequence

\(\frac{5}{7} = 0.714285 = 71.4285\)% --> same cycle but starts with the fifth smallest number (7) in the sequence

\(\frac{6}{7} = 0.857142 = 85.7142\)% --> same cycle but starts with the sixth smallest number (8) in the sequence

Reciprocal of 8 and its multiples

\(\frac{1}{8} = 0.125 = 12.5\)% --> Remember this as half of \(\frac{1}{4}\). From this you can easily derive all other multiples

\(\frac{2}{8} = \frac{1}{4} = 0.25 = 25\)%

\(\frac{3}{8} = 3*\frac{1}{8} = 0.375 = 37.5\)%

\(\frac{4}{8} = \frac{1}{2}= 0.5 = 50\)%

\(\frac{5}{8} = \frac{4}{8} + \frac{1}{8} = 0.5 + 0.125 = 0.625 = 62.5\)%

\(\frac{6}{8} = \frac{3}{4} = 0.75 = 75\)%

\(\frac{7}{8} = \frac{6}{8} + \frac{1}{8} = 0.75 + 0.125 = 0.875 = 87.5\)%


Reciprocal of 9 and its multiples

\(\frac{1}{9} = 0.1111 = 11.11%\)

\(\frac{2}{9} = 0.2222 = 22.22%\)

....
....

\(\frac{8}{9} = 0.8888 = 88.88%\)

I bet you will never forget it now!

Reciprocal of 10

Another easy one = 0.1

Though the link shared above has tips for bigger numbers, I am not sure how useful it will be to remember all of those. If interested you can visit the link.

Also, if you know any other trick that will help remember "stuff" please share below and we have everything in one place!




Great post!

Thank you!
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great tips!

wil surely try this.

:thanks
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Interesting info regarding fractions with base 7.

I use a neat trick to give me approximate value whenever I have fractions with base 7:

1. multiply the numerator of the fraction by 2
2. multiply number from step 1 by 7 and
3. place the number from step 2 after a decimal to get the approx value of the fraction

For example:
\(\frac{1}{7}\) \(\approx{0.14}\)
From step 1, multiply numerator by 2 to get 2
From step 2, multiply 2 by 7 to get 14
From step 3, simply place a decimal to get the value as approx. 0.14

\(\frac{2}{7}\) \(\approx{0.28}\)
From step 1, multiply numerator by 2 to get 4.
From step 2, multiply 4 by 7 to get 28
From step 3, simply place a decimal to get the value as approx. 0.28

similarly you can get
\(\frac{3}{7}\) \(\approx{0.42}\)
\(\frac{4}{7}\) \(\approx{0.56}\)
\(\frac{5}{7}\) \(\approx{0.7}\)
\(\frac{2}{7}\) \(\approx{0.84}\)

Note, all these are only approximate, so the result will be slightly smaller than actual value, but should be good enough for rough calculations.
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Thanks danlew!

This is definately something worth remembering. I am sure the text highlighted below is a typo and had to read - \(\frac{6}{7}\) \(\approx{0.84}\).

Also, very nicely explained :)

danlew
Interesting info regarding fractions with base 7.

I use a neat trick to give me approximate value whenever I have fractions with base 7:

1. multiply the numerator of the fraction by 2
2. multiply number from step 1 by 7 and
3. place the number from step 2 after a decimal to get the approx value of the fraction

For example:
\(\frac{1}{7}\) \(\approx{0.14}\)
From step 1, multiply numerator by 2 to get 2
From step 2, multiply 2 by 7 to get 14
From step 3, simply place a decimal to get the value as approx. 0.14

\(\frac{2}{7}\) \(\approx{0.28}\)
From step 1, multiply numerator by 2 to get 4.
From step 2, multiply 4 by 7 to get 28
From step 3, simply place a decimal to get the value as approx. 0.28

similarly you can get
\(\frac{3}{7}\) \(\approx{0.42}\)
\(\frac{4}{7}\) \(\approx{0.56}\)
\(\frac{5}{7}\) \(\approx{0.7}\)
\(\frac{2}{7}\) \(\approx{0.84}\)

Note, all these are only approximate, so the result will be slightly smaller than actual value, but should be good enough for rough calculations.
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danlew
Interesting info regarding fractions with base 7.

I use a neat trick to give me approximate value whenever I have fractions with base 7:

1. multiply the numerator of the fraction by 2
2. multiply number from step 1 by 7 and
3. place the number from step 2 after a decimal to get the approx value of the fraction

For example:
\(\frac{1}{7}\) \(\approx{0.14}\)
From step 1, multiply numerator by 2 to get 2
From step 2, multiply 2 by 7 to get 14
From step 3, simply place a decimal to get the value as approx. 0.14

\(\frac{2}{7}\) \(\approx{0.28}\)
From step 1, multiply numerator by 2 to get 4.
From step 2, multiply 4 by 7 to get 28
From step 3, simply place a decimal to get the value as approx. 0.28

similarly you can get
\(\frac{3}{7}\) \(\approx{0.42}\)
\(\frac{4}{7}\) \(\approx{0.56}\)
\(\frac{5}{7}\) \(\approx{0.7}\)
\(\frac{2}{7}\) \(\approx{0.84}\)

Note, all these are only approximate, so the result will be slightly smaller than actual value, but should be good enough for rough calculations.
Neat Trick. Thank you. Kudos Given.

Here is why this would work..
Let us assume that this is correct. Then,

\(\frac{x}{7}\) ~ \(\frac{(x * 2 * 7)}{100}\)

=> x ~\(\frac{(x * 2 * 7 * 7)}{100}\)

2 * 7 * 7 = 98

Therefore,
x ~ \(\frac{(x * 98)}{100}\)
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hotcool030
Great post yar. Thanks. Really it made life simpler.
There is another one missing from OP..

\(\frac{1}{11} = 0.09090..\)

Therefore, \(\frac{2}{11} = 0.1818..\)

\(\frac{3}{11} = 0.2727..\)

\(\frac{4}{11} = 0.3636..\)

And so on.
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Hello umg,

Thanks for bringing this up. I have edited the main post to include this. Also, changed the name of the thread to - Tips on remembering Reciprocals of firs few digits :-D

umg
hotcool030
Great post yar. Thanks. Really it made life simpler.
There is another one missing from OP..

\(\frac{1}{11} = 0.09090..\)

Therefore, \(\frac{2}{11} = 0.1818..\)

\(\frac{3}{11} = 0.2727..\)

\(\frac{4}{11} = 0.3636..\)

And so on.
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HI hotcool030,

Good to know that you found it useful! I myself am struggling with FDP problems - so, I can understand :)

hotcool030
Great post yar. Thanks. Really it made life simpler.
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