The formula is to take the rate per item times the number of items to equal the total.
(rate per item) X (number of items) = total
rate per item
number of items
total
miles per hour
number of hours
total miles
cents per coin
number of coins
total cents
dollars per ticket
number of tickets
total dollars
rate of interest per $ invested (%
changed to decimal)
number of $ invested
total $ interest earned
% salt per gallon
number of gallons
total gallons pure salt
Now I will demonstrate example #6 on the bottom of page 208 using a chart. (This problem is actually from the
beginning algebra book)
Dave needs a 10% acetic acid solution. After checking the storage room he finds that he only has a 5 % and a 20%
solution available. He decides to combine the two in order to reach a 10% mixture. How many liters of the 5% must he
add to 8 liters of the 20% solution to get a 10% result?
general headings
rate per item
number of items
total
specific headings
% of acid per liter (as
decimal)
number of liters
total liters pure acid
mixture 1 @5%
0.05
X
0.05X
mixture 2 @ 20%
0.20
8
0.20(8)
combined mixture @ 10%
0.10
X+8
0.10(X+8)
Now, we add the total liters of pure acid from mix 1 to the total liters of pure acid from mix 2 to get the total in the
combined mixture.
0.05X + 0.20(8) = 0.10(X+8)
The chart is step one of the word problem and the equation is step two and all that is left is doing the algebra for step three
and then finishing and answering the question asked in step four.