How could you use cross products to check the solution to this proportion $\frac{12}{30} = \frac{5}{x}$ $12/30=5/x$ ?

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Answer 1 · 2016-10-27T07:25:31

$12 \times 12.5 = 30 \times 5$ $12 xx12.5 = 30xx5$
$150 = 150$ $" "150=150$

You will have to have a solution first ..

Cross multiplying is a way of finding the solution, but we will use that to check later. Let's use another method to find $x$ $x$

$\frac{12}{30} = \frac{5}{x}$ $12/30 = 5/x$

Notice that $12 \div 2.4 = 5$ $12 div 2.4 =5$

$\frac{12 \div 2.4}{30 \div 2.4} = \frac{5}{12.5} \to x = 12.5$ $(12 div 2.4)/(30 div 2.4) = 5/12.5" " rarr x = 12.5$

To check whether this is correct: cross-multiply...

$\frac{12}{30} = \frac{5}{12.5}$ $color(lime)(12)/color(blue)(30) = color(blue)(5)/color(lime)(12.5)$

Is $12 \times 12.5 = 30 \times 5 ?$ $color(lime)(12 xx 12.5) = color(blue)(30xx5)?$

We find: $150 = 150$ $color(lime)(150) = color(blue)(150)$

Therefore we have the correct solution for $x$ $x$

This is true for any equivalent fractions:

$\frac{7}{5} = \frac{21}{15} \frac{4}{11} = \frac{20}{55}$ $7/5 = 21/15" " 4/11 = 20/55$

$105 = 105220 = 220$ $105 =105" "220 = 220$

How could you use cross products to check the solution to this proportion 1230=5x12/30=5/x?