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1st Year · Mathematics
Numbers · Decimal numbers

The generating fraction of a decimal number

A game on your phone says you have completed $0.75$ of a level. What exact fraction is that? Every terminating decimal can be written as a fraction. This fraction is called its generating fraction.

Generating fraction of a terminating decimal

Diagram showing the step from the terminating decimal 0.75 to the fraction 75/100 and its simplification to 3/4. 0.75 2 decimal places→ denominator 100 75/100 = 3/4
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In the Natural Sciences laboratory, you have weighed a sample of sand and the scale reads $0.75$ grams. Write this number as a decimal fraction (with a power of 10 in…

In the Natural Sciences laboratory, you have weighed a sample of sand and the scale reads $0.75$ grams. Write this number as a decimal fraction (with a power of 10 in the denominator) and then simplify it to obtain its irreducible generating fraction.

Solve
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Calculate the generating fraction of the following terminating decimal numbers. Remember to simplify the result wherever possible: a) $0.5$ b) $1.2$ c) $0.25$ d) $0.08$

Calculate the generating fraction of the following terminating decimal numbers. Remember to simplify the result wherever possible:

  1. a) $0.5$
  2. b) $1.2$
  3. c) $0.25$
  4. d) $0.08$
Solve
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On offer in a music shop, a digital album costs $9.90$ €. Express the price of the album as a fraction of natural numbers and simplify it until it cannot be reduced any…

On offer in a music shop, a digital album costs $9.90$ €. Express the price of the album as a fraction of natural numbers and simplify it until it cannot be reduced any further.

DIGITAL ALBUM €9.90 OFFER ? ?
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Going further: generating fraction of a recurring decimal

Explanatory diagram for obtaining the generating fraction with nines in the denominator from a recurring decimal whose repeating block starts straight after the decimal point. 0.6666… (repeating 6) recurring block of 1 digit→ one 9 in the denominator 6/9 = 2/3

Recurring decimals with a non-recurring part

When there are digits before the recurring block (the non-recurring part), the rule extends a little.

Visual diagram breaking 2.16 recurring into its non-recurring part and recurring block to set up the subtraction in the numerator. 2.1666… (repeating 6) decimal part .1666…: non-recurring 1,recurring block 6 decimal part: (16−1)/90 = 1/6so 2.1666… = 2 + 1/6 = 13/6

Back to the start: $0.75 = \frac{75}{100} = \frac{3}{4}$, so you have completed exactly three quarters of the level. (Extension: if the game had said $0.\dot{6}$, one repeating digit gives $\frac{6}{9} = \frac{2}{3}$, two thirds of the level.)

Summary

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