ISEE Lower Level Math : How to subtract

Study concepts, example questions & explanations for ISEE Lower Level Math

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Example Questions

Example Question #1 : How To Subtract

Henry had $538.23 in his checking account at the bank before he went shopping. At the mall, he spent $43.91 at one store and $71.84 at another store. How much money does Henry have left in his bank account?

Possible Answers:

$423.48

$422.48

$423.52

$422.84

Correct answer:

$422.48

Explanation:

To find the difference, you must subtract. But first you must add the two amounts he spent at the mall:

 

\(\displaystyle $43.91 + $71.84 = $115.75\)

 

Now subtract. Line up the numbers vertically. Remember to use the rules of borrowing to subtract.

 

\(\displaystyle $538.23-$115.75=$422.48\)


Henry now has $422.48 in his bank account.

Example Question #312 : Numbers And Operations

Evaluate:

\(\displaystyle -50+32+(-11)\)

Possible Answers:

\(\displaystyle 32\)

\(\displaystyle -29\)

\(\displaystyle 71\)

\(\displaystyle -7\)

Correct answer:

\(\displaystyle -29\)

Explanation:

\(\displaystyle -50+32+(-11)\)

\(\displaystyle -50+32\) is the same as \(\displaystyle 32-50=-18\).

\(\displaystyle -18+(-11)=-18-11=-29\)

Example Question #313 : Numbers And Operations

The total combined weight a 4 boxes is 25 lbs. Box A weighs 4 lbs, box B weighs 10 lbs, and box D weighs 6 lbs. How much does box C weigh?

Possible Answers:

6 lbs

12 lbs

5 lbs 

4 lbs

10 lbs

Correct answer:

5 lbs 

Explanation:

To find the weight of box C, subtract the weight of the other three boxes from the total weight. 

Box C = Total - Box A - Box B - Box D

Box C = 25 lbs - 4 lbs - 10 lbs - 6 lbs

Box C = 5 lbs 

Example Question #2 : How To Subtract

Solve the following number sentence.

\(\displaystyle 10 - 4 + (4 \times 2) - 2^{3}\)

Possible Answers:

\(\displaystyle 6\)

\(\displaystyle 12\)

\(\displaystyle 8\)

None of the other answers.

\(\displaystyle 14\)

Correct answer:

\(\displaystyle 6\)

Explanation:

To successfully solve this question, the order of operations must be used.

There are 4 steps in the order of operations and they are as follows:

1. P - Solve all problems within a parentheses.

2. E - Solve any numbers that have an exponent.

3. MD - From the left side of the problem to the right side of the problem solve all Division and Multiplication.

4. AS - From the left side of the problem to the right side of the problem solve all Subtraction and Addition.

 Based on the rules the first part of the problem to be solved is \(\displaystyle (4 \times 2)\) as it is in parentheses.  The other parts of the problem remain the same and are re-written until their step is reached. \(\displaystyle [ 4 \times 2 = 8]\)

\(\displaystyle 10 - 4 + 8 - 2^{3}\)

Next the exponent is to be solved.  The exponent number in this problem is \(\displaystyle 2^{3}\)which means to multuply the base to itself \(\displaystyle 3\) times.

\(\displaystyle [ 2 \times 2 \times 2 = 4 \times 2 = 8]\)

\(\displaystyle 10 - 4 + 8 - 8\)

Next looking from the left to the right of the problem there are no multiplication or division calculations to do so skip to the last step.

Finally, starting from the left side of the problem and moving to the right side of the problem each set of two numbers will be solved until the final answer is reached.  Starting with \(\displaystyle 10 - 4 = 6\) then \(\displaystyle 6 + 8 = 14\) and lastly \(\displaystyle 14 - 8 = 6\).

The final answer would be \(\displaystyle 6\).

Example Question #3 : How To Subtract

Sam is shipping five boxes, which weigh 50 pounds in total. The first four boxes weigh 8 pounds, 12 pounds, 9 pounds, and 15 pounds. How much does the last box weigh?

Possible Answers:

\(\displaystyle 6\ pounds\)

\(\displaystyle 10\ pounds\)

\(\displaystyle 14\ pounds\)

\(\displaystyle 13\ pounds\)

\(\displaystyle 5\ pounds\)

Correct answer:

\(\displaystyle 6\ pounds\)

Explanation:

First, add the first four boxes together:

\(\displaystyle 8+12+9+15=44\)

Now, subtract this number from the total to find the weight of the remaining box:

\(\displaystyle 50-44=6\)

Example Question #4 : How To Subtract

Evaluate:

\(\displaystyle -14-12+(-5)+3\)

Possible Answers:

\(\displaystyle -28\)

\(\displaystyle 6\)

\(\displaystyle 0\)

\(\displaystyle -14\)

\(\displaystyle -18\)

Correct answer:

\(\displaystyle -28\)

Explanation:

First, adding negative numbers is the same as subtracting them:

\(\displaystyle -14-12-5+3\)

Now subtract:

\(\displaystyle -31+3=-28\)

Example Question #5 : How To Subtract

Mark went to the grocery store to buy ingredients to make a cake. He bought eggs for $2.99, flour for $4.99, sugar for $3.99, and butter for $2.50. If he paid the cashier with a $20 bill, how much money did he recieve in change?

Possible Answers:

\(\displaystyle \$5.50\)

\(\displaystyle \$5.53\)

\(\displaystyle \$4.53\)

\(\displaystyle \$14.47\)

\(\displaystyle \$15.47\)

Correct answer:

\(\displaystyle \$5.53\)

Explanation:

Since the question is asking how much money did Mark have left over, we need to subtract the cost of each item he bought from $20.

There are two ways of solving this problem:

  • We can add up the cost of all the ingredients and then subtract the total cost from $20.00

\(\displaystyle \small 2.99+4.99+3.99+2.50=14.47\)

\(\displaystyle \small 20-14.47=5.53\)

  • We can subtract the cost of each item from $20.00. Note, if we choose to solve the problem this way, we must follow order of operations and go from left to right     

\(\displaystyle \small 20-2.99-4.99-3.99-2.50=5.53\)

\(\displaystyle \small 20-2.99=17.01\)

\(\displaystyle \small 17.01-4.99=12.02\)

\(\displaystyle \small 12.02-3.99=8.03\)

\(\displaystyle \small 8.03-2.50=5.53\)

Example Question #317 : Numbers And Operations

Solve:

\(\displaystyle \small (15-2)*3-4-6=\)

Possible Answers:

\(\displaystyle -91\)

\(\displaystyle -1\)

\(\displaystyle 29\)

\(\displaystyle 25\)

 

\(\displaystyle -19\)

Correct answer:

\(\displaystyle 29\)

Explanation:

In order to solve this problem, you must follow order of operations. One way of remembering the correct order is to remember the acronym PEMDAS. PEMDAS reminds you what you need to do first.

  • P = Parentheses
  • E = Exponents
  • M = Multiplication
  • D = Division
  • A = Addition
  • S = Subtraction

Note: For Multiplication and Division, and Addition and Subtraction, you do whatever operation comes first from left to right. So, if subtraction comes before addition, you do the subtraction first.

In this question, you are asked to solve:  \(\displaystyle \small \small (15-2)*3-4-6\)

First, we subtract \(\displaystyle \small 2\) from \(\displaystyle \small 15\) since it is in the parenthesis (PEMDAS)

\(\displaystyle \small \small 15-2=13 \rightarrow\)

\(\displaystyle \small 13*3-4-6\)

Second, we multiply \(\displaystyle \small 13\) by \(\displaystyle \small 3\) (PEMDAS)

\(\displaystyle \small 13*3=39\rightarrow\)

\(\displaystyle \small \small 39-4-6\)

Third, we subtract \(\displaystyle \small 4\) from \(\displaystyle \small \small 39\). We subtract \(\displaystyle \small 4\) from \(\displaystyle \small \small 39\) first because we have to go from left to right (PEMDAS)

\(\displaystyle \small \small 39-4=35\rightarrow\)

\(\displaystyle \small 35-6\)

Lastly, we subtract \(\displaystyle \small 6\) from \(\displaystyle \small 35\) to get the answer.

\(\displaystyle \small \small 35-6=29\)

Example Question #6 : How To Subtract

Sally bought 3 different picture frames and paid a total of $60. If the first frame cost $15 and the second frame cost $25, how much did the third frame cost?

Possible Answers:

\(\displaystyle \$30\)

\(\displaystyle \$25\)

\(\displaystyle \$20\)

\(\displaystyle \$15\)

\(\displaystyle \$10\)

Correct answer:

\(\displaystyle \$20\)

Explanation:

In order to find out how much the third frame costs, we need to subtract the cost of the first two frames ($15 and $25) from the total amount ($60).

There are two ways to subtract the cost of the first two frames from the total amount:

Method 1

We can subtract the total amount spent on the first two frames from $60 \(\displaystyle \rightarrow\)

\(\displaystyle 60-(Frame_{1}+Frame_{2})\)                                                      

Remember to follow Order of Operations (PEMDAS) and add the numbers in parenthesis first.

\(\displaystyle 60-(15+25)\)

\(\displaystyle 60-40=20\)

The cost of the third frame was $20

Method 2

We can subtract the cost of each frame from $60

\(\displaystyle \rightarrow\) \(\displaystyle 60-Frame _{1}-Frame_{2}\)

\(\displaystyle 60-15-25\)

\(\displaystyle 45-25=20\)

The cost of the third frame was $20

Example Question #7 : How To Subtract

Which of the following numbers can complete the sequence below?

\(\displaystyle \left ( 29, 26, 23, 20, x\right )\)

Possible Answers:

\(\displaystyle 16\)

\(\displaystyle 21\)

\(\displaystyle 18\)

\(\displaystyle 17\)

Correct answer:

\(\displaystyle 17\)

Explanation:

In this sequence, each subsequent number is 3 less than the previous number. Given that 3 less than 20 is equal to 17, the correct answer is 17. 

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