cooking rice

A cook bought 100 pounds of rice. If he used 4/5 of it in cooking, how many pounds of rice did he use?

 

Similar problems worksheets

Answer:

From “used 4/5  of it in cooking” the word after “used 4/5  of” is “it” or “100 pounds of rice” so the amount rice bought is the amount in 1 (whole).

4/5 of 100 pounds of rice were used in cooking so we multiply the amount in 1 ( whole ), 100 pounds, with the fractional part used,4/5  , to find the amount in this part, the amount of rice used:

4/5x 100=80 pounds

 

 

 

 

 

 

parenthesis and multiplication in one expression: which operation should be taken care of first?

Order of operations ( in order to make the explanation easy to understand, simple numbers are used)

Without any other operations in an expression: Addition and subtraction are equal operations in the way that is “first come, first served” from left to right:

12+3-9-5

=15-9-5

=6-5

=1

Without any other operations in an expression: multiplication and division are equal operations in the way that is “first come, first served” from left to right:

12 ÷6×3

= 2 ×3

=6

 

When an expression has addition and (or) subtractions with multiplication and (or) divisions in it, multiplications and ( or divisions) should be done first; additions and (or) subtractions should be done afterwards.

 34- 9×3

=34- 27

=7

 

2+ 4 ×5 – 3×7

=2+ 20- 21

=22-21

=1

 

When an expression has parenthesis first, the operations in the parenthesis should be done first and other operations need to follow the rules above.

2+ 4 × (5 – 3) ×7 (operation in the parenthesis is done first)

=2+4 × 2×7 (multiplication is done before addition)

=2+ 8 × 7 (first multiplication is done , now let’s do the second multiplication)

=2+56

=58

Worksheets for similar problems

 

Order of operations

Many teachers do not emphasize “order of operation”, but “order of operations” is very important. Without knowing order of operations well, you do not know how to solve a math problem.

Some examples are given in the following, There are also worksheets for you to work on after you understand the examples.

Order of operations ( in order to make the explanation easy to understand, simple numbers are used)

Without any other operations in an expression: Addition and subtraction are equal operations in the way that is “first come, first served” from left to right:

12+3-9-5

=15-9-5

=6-5

=1

Without any other operations in an expression: multiplication and division are equal operations in the way that is “first come, first served” from left to right:

12 ÷6×3

= 2 ×3

=6

 

When an expression has addition and (or) subtractions with multiplication and (or) divisions in it, multiplications and ( or divisions) should be done first; additions and (or) subtractions should be done afterwards.

 34- 9×3

=34- 27

=7

 

2+ 4 ×5 – 3×7

=2+ 20- 21

=22-21

=1

 

When an expression has parenthesis first, the operations in the parenthesis should be done first and other operations need to follow the rules above.

2+ 4 × (5 – 3) ×7 (operation in the parenthesis is done first)

=2+4 × 2×7 (multiplication is done before addition)

=2+ 8 × 7 (first multiplication is done , now let’s do the second multiplication)

=2+56

=58

 Worksheets for you to work on 

 

cutting a stick

Can you solve this problem?

1/8 of a stick is cut off. If If another stick that is 15 inches long is glued to the remaining part of the first stick, the first stick will be 1/2 longer than its original length. What is the original length of the first stick?

In this problem, you need to find the match between the fractional part and the amount in it ( if you do not know about these terms, please go to Word Problem: Detailed Explanations of Reasoning and Solving Strategies Volumes 11-A, 11-B and 12)

15 inches  not only has covered  1/8 of the stick that is cut off but also makes the  the stick 1/2 longer so we can say that 15 inches match the sum of the fractional parts: 1/8 and 1/2.

We divide the sum of the fractional parts: 1/8+1/2=5/8 into the amount that matches it: 15 inches to find the amount in 1, which is the length of the original stick: ( please go to the books Word Problem: Detailed Explanations of Reasoning and Solving Strategies Volumes 11-A, 11-B and 12 for more detailed explanation):

15÷5/8=24 inches

The original stick is 24 inches. 

 

multiplications with 0’s in the end of the factors and products

Look at the following equations:

1. 70 x 4=280

2. 70 x 40=2,800

3. 700 x 4=2,800

4. 700 x 40=28,000

5. 7,000 x 40=280,000

What can we learn from the above equations?

All the equations have four numbers in common: 7 , 4 , their products, 28 and 0’s.

Here is the trick: when you try to get the answer of 7,000 x 40, you only need to take two steps:

First: Find the product of 7 and 4, which is 28;

Secondly: count the number of 0’s in both 7,000 and 40, which is 4; put the four 0’s after 28.

Therefore, the product of 7,000 and 40 is 280,000

The last thing that you want to do is to multiply 0’s by 0’s in the numbers.