How to add and subtract decimals
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HSPT Math › How to add and subtract decimals
Explanation
To subtract decimals you place the first decimal over the top of the other aligned by the decimal point. If there are no numbers after a tens, hundredths, or thousandths place or further to the right of the decimal just add a zero in the required areas.
For example 
Then go through each place and subtract the top number by the bottom number. Subtract the numbers in each place like you would any number.
The example we are working with will look like this
The answer after subtraction is
The above is a menu at the concession stand at a drive-in movie.
Gary wants to order two hamburgers and two small orders of fries. He wants to order two sodas of the same size. If he has just a twenty-dollar bill on hand, what is the largest size soda of which he can order two?
Gary can afford two large sodas
Gary can afford two medium sodas, but not two large sodas
Gary can afford two small sodas, but not two medium or large sodas
Gary cannot afford two sodas
Explanation
The easiest way to think of this is to note that Gary seems to be ordering for two people, himself and a friend. He has $20, so half of this will be for himself and half for his friend - and half of $20 is $10.
Each hamburger costs $4.89, and each small order of fries costs $2.29. This leaves
to spend on a soda for each person. This will enable to him to buy both himself and his friend a large soda.
What is 16.7548 rounded to the nearest tenth?
Explanation
The tenth's place is the position one unit to the right of the decimal point. In this case, that is the 7.
After identifying the position, we need to determine if this number remains 7 or if we need to round it up to 8. If the number to the right of the tenth's place is 4 or lower, then our number will remain 7. If it is 5 or greater, then we will round the 7 up to 8.
In this case, the number is indeed 5, so our tenth's place becomes 8. All numbers to the left of the tenth's place will remain the same.
Evaluate:
Explanation
Add the first two numbers, making sure you align the decimal points in the addends and the sum:
Now subtract the third number, making sure you again align the decimal points:
A runner runs 10.2 miles east, then 2.3 miles west, then 1.4 miles east.
How many miles did the runner travel from where he started? (How far east did the runner go)?
9.3 miles
10.2 miles
6.5 miles
13.9 miles
19.3 miles
Explanation
When the runner is travelling east, it's in the positive direction. West is the negative direction. So we can compute it by doing the operation 10.2 + (–2.3) + 1.4 = 9.3
If Susie bought a pair of shoes for 
Explanation
You add all three values and you get 
Jenny is getting ready for school. She bought school supplies on a tax-free day. She bought notebooks for $1.25 each and crayons for $0.90 each. Jenny bought two more notebooks than crayons. She paid with a ten dollar bill and got $1.05 in change. How many notebooks did she buy?
4
3
1
2
5
Explanation
Define variables as x = number of crayons and x + 2 = number of notebooks
To find out how much she spent, we subtract her change from what she paid with: 10.00 – 1.05 = 8.95
Then we need to solve the problem cost of notebooks plus the cost of crayons equals the total cost.
1.25(x + 2) + 0.90x = 8.95 and solving for x gives 3 crayons and 5 notebooks
Above is the menu at the concession stand at a school carnival. Ken wants to purchase a hamburger, a medium order of fries, and medium soda for himself, and a hot dog, a small order of fries, and a small soda for his friend Donna. He hands the clerk a $10 bill and a $5 bill. He has some $1 bills in his pocket; how many of them will he need to hand to the clerk along with the other two bills?
(No tax is charged, since this is a school event)
Three
Two
One
None
Explanation
The items Ken purchases are as follows:
Hamburger: $4.89
Medium fries: $2.79
Medium soda: $1.69
Hot dog: $4.39
Small fries: $2.29
Small soda: $1.09
The sum of the prices of these items:
Subtract from $20:
Rounding this up - Ken needs to give the clerk three more $1 bills.
Subtract:
Explanation
Rewrite 
The menu of a local coffeehouse reads as follows:
Sandy orders some drinks for herself and some friends. She orders three cappuccinos, two iced teas, two cafe lattes, and an espresso. The sales tax is five percent. How much change does she receive back for a twenty-dollar bill?
A twenty-dollar bill isn't enough to buy the drinks.
Explanation
The three cappuccinos cost:
The two iced teas cost
The two cafe lattes cost
The espresso costs 
Add these amounts to get the cost before tax:
The tax is five percent of 
Add both values in order to obtain the total cost after tax.
As a result, the change from a twenty-dollar bill is as follows:
