# the number of students in the second grade is 1.2 times the number of students in the first grade

The total number of first graders and second graders in an elementary school is 330. If the number of students in the second grade is 1.2 times the number of students in the first grade, how many students are in each grade?

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# Cylinder, again

The diameter of the base of a cylinder barrel is 20 inches. If it is 25 inches deep, what is the volume of the cylinder barrel?

# Finding the surface area of a cylinder

The diameter of one of a cylinder’s bases is 5 inches. If the cylinder is 20 inches high, what is the surface area of the cylinder?

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Granddad raises a total of 18 black rabbits and white rabbits. If the number of white rabbits is 5 times the number of black rabbits, how many of each type does Granddad have?

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# the area of the lateral surface of a cylinder

The diameter of one of a cylinder’s bases is 3.2 feet. If the cylinder is 5 feet high, what is the area of the lateral surface?

# sum of fractions into sum of amount to find the amount in 1

Granddad raises a total of 18 black rabbits and white rabbits. If the number of black rabbits is 1/5 of the number of white rabbits, how many of each type does Granddad have?

# the greatest common factor—question and answer

Three  ropes  are  120  inches  long,  90  inches  long  and  150 inches  long.  They are cut into sections with no remaining parts.  If each section has the same length, what is the largest possible length for each section?  How  many  sections  can  we  get  altogether?

Worksheets for this type of questions

Since each section has the same length, that means we need to find the common factors of 120, 90 and 150. Since we need to find the largest possible length of each section, we need to find the greatest common factor. That is 30. So the largest possible length of each section is 30 inches.

The  rope  that  is  120  inches  long  is  cut  into  4  sections. The  rope  that  is  90  inches  long  is  cut  into  3  sections. The  rope  that  is  150  inches  long  is  cut  into  5  sections. Therefore, all the ropes are cut into a total of 12  sections.

# the least common multiple and the greatest common factor

The  product  of  two  natural  numbers  is  420.  If  their greatest  common  factor  is  12,what  is  their  least  common multiple?

According  to  this  rule:  The  product  of  the  greatest  common factor  and  the  least  common  multiple  of  the  two  numbers  equals to  the  product  of  the  two  numbers

The  least  common  multiple  of  the  two  numbers  is:  420÷12=35

# Average Speed

Lisa and Sarah were given a word problem to work on:

The distance between City A and City B is 360 miles. A car was going at 60 miles per hour from City A to City B; on the way back, the car was going at  40 miles  per hour because it was raining really hard so that driver could not see very well. What was the average speed of the car for the round trip?

(60+40)÷2=50 miles per hour

Sarah said: “No, you cannot solve the problem like that. This is how to solve it.”

The total distance for the round trip: 360×2=720 miles

The amount of time the car used to travel from City A to City B:

360÷60=6 hours

The amount of time the car used to travel back to City A from City B:

360÷40=9 hours

The total amount of time for the round trip:

6+9=15 hours

The average speed for the round trip= the total distance for the round trip÷ the total amount of time spent on the round trip= 720÷15=48 miles per hour

Friends, I believe that you all think that Sarah is right and she is. Remember: when you solve a word problem on travelling, finding the average speed is not the same as finding the average age, the average height, etc.

# cutting a stick

A stick is 1 yard long. If 1/5 is cut off at first, 1/6 of the remaining section is cut off secondly, 1/7 of the last remaining section is cut off thirdly and the cutting keeps on until 1/10 of the last remaining section is cut off finally, what is the length of the remaining stick?
The solution to this type of question usually has a pattern:

When 1/5 is cut off, 4/5 yard is left;

When 1/6 of the remaining section is cut off, 5/6 of 4/5 yard is left:

4/5 yard × 5/6 =4/6 yard

When 1/7 of the last remaining section is cut off, 6/7 of 4/6 yard is left:

6/7  × 4/6 = 4/7 yard

In this pattern, when 1/10 of the last remaining part is cut off, the amount left should be:

4/10 yard= 2/5 yard ( simplest term)