Ratios in word problems
Many math word problems come down to simple ratios. What's key is how to set the problem up. Take the following example. Jill wants to keep her ratio of expenses to savings at 2:4. That means for every $2 spent, she wants to save $4. If her income for the week is $950, how much will she save? When you see a problem like this...ratio...think fraction. Simply add the two numbers showing. In this case, 2 + 4 = 6. That becomes your denominator. Since the ratio is expenses to savings, the numerator is 2 (expenses), and the fraction 2/6 represents the fraction of the total income that are expenses. So, if the total income is $950, 2/6 x 950 = 316.67 represents the amount of expenses. Therefore, savings must be 950 - 316.67 = $633.33.
So, for every $2 she spends, she saves $4 means that she's roughly saving twice what she spends. Notice that $633.33 = 2 x $316.67. So, it makes sense!
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