Worksheet: Guesstimation | Mental Mathematics for Class 8 PDF Download

Fill in the Blanks

Q1: The guesstimation method for addition involves rounding the original numbers __________.

Q2: To estimate the total cost while shopping, you can round prices to the nearest __________.

Q3: When estimating the square root of a number, you aim to find a number that, when multiplied by itself, approximates the original number. This number is called the __________.

Q4: The Rule of 70 is used to estimate how long it takes for money to __________.

Q5: When paying off a loan, the monthly interest rate is usually the annual interest rate divided by __________.

Q6: The Rule of 110 helps estimate how long it takes for your money to __________.

Q7: To calculate a 7.75% sales tax, you can approximate it as slightly less than __________%.

Q8: The formula to estimate the monthly payment for a loan of $P in N months with a monthly interest rate of i is M ≈ __________.

Q9: The square root of most numbers is not a whole number, so your estimate is likely to contain a __________ or decimal point.

Q10: The relative error in guesstimation methods should ideally be kept __________ for accurate estimates.

Multiple Choice Questions

Q1: What is the main advantage of using Snapchat's temporary messages?
(a) Messages are saved indefinitely
(b) Messages can be viewed by anyone
(c) Messages are easy to share with friends
(d) Messages disappear after being viewed

Q2: What is the Rule of 70 used for?
(a) Estimating square roots
(b) Calculating sales tax
(c) Estimating how long it takes money to double
(d) Finding the square of a number

Q3: When rounding numbers in guesstimation, what should you aim for to improve accuracy?
(a) Round up both numbers
(b) Round down both numbers
(c) Round in opposite directions
(d) Don't round numbers

Q4: What is the approximate monthly interest rate if the annual interest rate is 6%?
(a) 0.06
(b) 0.5
(c) 0.005
(d) 0.5%

Q5: How can you estimate the square root of a number like 87?
(a) Divide by 10
(b) Divide by 9
(c) Take the average of 9 and 10
(d) Divide by 2

True and False

Q1: True/False: Snapchat's messages are permanent and can be viewed multiple times.

Q2: True/False: The Rule of 70 helps estimate how long it takes money to quadruple.

Q3: True/False: To improve accuracy in guesstimation, it's better to round both numbers in the same direction.

Q4: True/False: The monthly interest rate is typically higher than the annual interest rate.

Q5: True/False: The square root of most numbers is a whole number.

Short Answer Questions 

Q1: Explain the main advantage of using Snapchat's temporary messages.

Q2: Describe how to estimate the total cost while shopping using guesstimation.

Q3: How can you estimate the square root of a number using guesstimation? Provide an example.

Q4: Explain the Rule of 70 and provide an example.

Q5: How can you estimate the monthly payment for a loan using a monthly interest rate of i, borrowed amount P, and a loan term of N months?

Q6: Explain how to estimate sales tax for a purchase using a given percentage.

Q7: What is the Rule of 110, and how does it work?

Q8: Explain how to estimate a 7.75% sales tax using the Rule of 70 and a 6% annual interest rate.

Q9: Why might the square root of most numbers not be a whole number?

Q10: In guesstimation, why is it important to keep the relative error small when making estimations?