**High School Number Sense Lesson 27: Money Calculations with Ratios**

I've been waiting a long time to introduce the topic of money to this blog--my education is in Personal Finance.

**Consumer problems**cause a lot of stress in society, but they don't have to cause stress on a number sense test. Today's concept is actually quite useful to anyone who shops. It showed up a whopping

**18 times**this year in high school, on average at

**question # 24**.

**Number Dojo Level: 121**

The idea behind this concept is that you are given a price for a certain number of items. You are asked to calculate the price for a different number of the same item. For example,

**if A apples cost $C, then B apples cost $___.**

**How to Solve:**

- Divide the cost (
**C**above) by the # of given items (**A**above). This gives you the "each" cost. - Multiply the "each" cost by the # of items they're wanting (
**B**above). - Write the answer in dollars and cents--with
**2 decimal places**(even if the answer has fewer). Any money problem on a number sense test has to be written with 2 decimal places. The $ will be given in front of the answer blank,**so don't write a $**.

**C x B/A**. There will often be an opportunity to cancel out common factors in any of these numbers, which will make the calculations easier. And remember my motto:

**divide before you multiply!**

**Example 1: If 6 pens cost $1.44, then 10 pens cost $___**

- Think of this as $1.44 ÷ 6 x 10, or
**$1.44 x 10/6**. - Divide first. $1.44 ÷ 6 =
**$0.24**. - Then multiply. $0.24 x 10 = $
**2.40**. (Remember to write 2 decimal places).

**Example 2: If 14 cups cost $8.00, then 35 cups cost $___**

- Think of this as $8.00 ÷ 14 x 35, or
**$8.00 x 35/14**. - $8.00 x 35/14 reduces to
**$8.00 x 5/2**. - Divide first $8.00 ÷ 2 =
**$4.00**. - Then multiply. $4.00 x 5 = $
**20.00**. (Remember to write 2 decimal places).

**Example 3: If 4 bananas cost $0.78, then two dozen bananas cost $___**

- Think of this as $0.78 ÷ 4 x 24, or
**$0.78 x 24/4**. (There are 12 items in a dozen, so 2 dozen = 24). - $0.78 x 24/4 =
**$0.78 x 6**. - $0.78 x 6 = $
**4.68**.

**Example 4: If 7 CDs cost $42.28, then 5 CDs cost $___**

- Think of this as $42.28 ÷ 7 x 5, or
**$42.28 x 5/7**. - Divide first. $42.28 ÷ 7 =
**$6.04**. - Then multiply. $6.04 x 5 = $
**30.20**. (Remember to write 2 decimal places).

**Example 5: If 5 tadpoles cost $1.30, then 5 dozen tadpoles cost $___**

- Think of this as $1.30 ÷ 5 x 60, or
**$1.30 x 60/5**. - $1.30 x 60/5 reduces to
**$1.30 x 12**. - $1.30 x 12 = $
**15.60**. (Remember to write 2 decimal places).

**Here's a free worksheet to help you practice MoneyRatio:**

moneyratio.pdf |

**Up Next for High School: NumPosIntDiv**