2*x :5 *y

3: < >

< > = (3

*5*y) / 2*x

so how do I know from what is written in <> the amount of sugar for making amount of cake 3?! thanks beforehand

- Thread starter Ryan$
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2*x :5 *y

3: < >

< > = (3

so how do I know from what is written in <> the amount of sugar for making amount of cake 3?! thanks beforehand

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I think it's better to say "to" instead of "vs".… [ratio] 2:5 [describes] amount of cake vs amount of sugar …

2:5 denotes the ratio 2 parts cake to 5 parts sugar

You don't need symbol x for the amount of cake because you already said it's 3.… how much [sugar is needed if] amount of cake is 3 …

… [let's] assume x is the amount of cake …

You can find the sugar amount by solving a simple proportion.

\(\displaystyle \dfrac{2}{5} = \dfrac{3}{?}\)

Multiply on the diagonal and then divide by the number not used.

5 × 3 ÷ 2 = 7.5

You need 7.5 parts sugar for every 3 parts cake.

Check:

2/5 = 0.4

3/7.5 = 0.4

In other words, 2/5 = 3/7.5

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Some examples of writing two ratios and setting them equal to each other to solve proportion word problems.

www.khanacademy.org

Learn the reasoning behind solving proportions. We'll put some algebra to work to get our answers, too.

www.khanacademy.org

Confused by notation and terminology related to ratios? This lesson provides clear definitions and worked examples.

www.purplemath.com