Ms. Ryan MCATC Medical Math

 A ratio is composed of 2 related numbers separated by a colon.  A statement of how two numbers compare.  A comparison of the size of one number to the size of another number.  Expressed as "a to b" or a : b  Example: 1000 mL : 1 L

 Used to compare two ratios or make equivalent fractions.  A comparison between two values.  Shows the relationship between 2 equal ratios.  It consists of 2 ratios separated by an = sign which indicates the 2 ratios are equal.  Example: 1000 mg :1 g = 2000 mg : 2 g  The units of measurement in the 2 ratios of a proportion must be expressed in the same sequence.  Correct Example: 1000 mg : 1 g = 2000 mg : 2 g  Incorrect Example: 1000 mg : 1 g = 2 g : 2000 m

 The means-extremes property of proportions allows you to cross multiply or set up an equation, taking the product of the means and setting them equal to the product of the extremes.  The numbers on the ends of a proportion are called the extremes Example: 1000 mg : 1 g = 2000 mg : 2 g  The numbers in the middle are called the means. Example: 1000 mg : 1 g = 2000 mg : 2 g

 To make a proportion a true statement the product of the means must equal the product of the extremes.  Known quantities and unknown quantiles  Example: 1500 mg = x g  Known quantity is 1000 mg = 1 g  Unknown quantity is 1500 mg = x g  Then you have 1000 mg : 1 g = 1500 mg : x g

 1000 mg : 1 g = 1500 mg : x g  Multiply the extremes  1000 X x = 1000 x  Multiply the means  1 X 1500 = 1500  Set up the equation  1000 x = 1500  Solve for x by dividing both sides by 1000  1000 x =  x = 1.5 g  Now you have a true statement  1000 mg : 1 g = 1500 mg : 1.5 g

1. Multiply the unit to by changed by L = _______ ml 2 x 1000 = L = 2000 ml 2. Move the decimal point of the unit to be changed 3 places to the right 2.0 would become or 2000 ml 2. Ratio & proportion 1 L = 1000 ml : 2 L = x ml multiply the means (the inner) 1000 x 2 = 2000 multiply the extremes (the outer) 1 X x ml = x ml 2000 = x ml

1. Divide the unit to by changed by mg = _______ g 250 ÷ 1000 = mg = 0.25 g 2. Move the decimal point of the unit to be changed 3 places to the left 250 mg would become 0.25 g 3. Ratio & proportion 1 g = 1000 mg : x g = 250 mg multiply the means (the inner) 1000 X x g = 1000 x multiply the extremes (the outer) 1 X 250 = x = x = 0.25 g

 Example: 4 kg = _____ lbs  Known quantity 1 kg = 2.2 lbs  Unknown quantity x lbs = 4 kg  1 kg : 2.2 lbs = 4 kg : x lbs  2.2 x 4 = 8.8  1 X x = x  X = 8.8 lbs

 16 oz : 1 pt = 64 oz : x pt  16 oz : 1 pt = 64 oz : x pt-multiply the extremes 16x  16 oz : 1 pt = 64 oz : x pt – multiply the means and you get 64  Set up to solve for x- 16x = 64