Fri 13th Jan – Using Estimating skills to help answers make sense

LEARNING OBJECTIVE: Understand how we can use estimates of answers to check we have not made silly mistakes in a calculation (especially when using a calculator)
SUCCESS CRITERIA: You will be able to estimate the solution to a problem
STARTER: Without using a calculator can you work out which of the following sums are definitely incorrect

1. 42 x 68 = 28 560
2. 568 ÷ 26 = 218.46
3. 34 x ( 6.7 + 45.7) = 1781.6
4. 27 x 45 x 2.3 = 4536.5

LESSON: Encourage discussion on how students found answers to above questions
Work through the first screen from this Mymaths Lesson, use questions on screen 2 (many times if necessary) to give students practice
Use the problems on screen 4 & 5 to extend students skills using estimating on real problems
EXTENSION: More problems to use estimation skills
Exercise 2
1) The number of boys in a school is 456 and the number of girls is 512.
a) Round off both numbers to the nearest 100 and estimate the total number of pupils at the school.
b) Round off both numbers to the nearest 10 and do a similar estimate.
2) A theatre has 37 rows each with 22 seats. The total number of seats is 37 
a) Write down the numbers you would use to get an estimate of the answer.
b) Calculate this estimate.
A CD player costs £167 and a TV costs £280. What simple calculation would you do to show that the total cost is less than £500?
A jar of jam costs 57p, a tub of margarine costs 48p and a bottle of sauce costs 77p.
What simple calculation would you do to show that the total cost is less than £2.00?
Tickets for a concert cost £5.75 each. A group of 18 people went to the concert.
What simple calculation would you use to show that the total cost is less than £120?
I travel 57 miles from home to Birmingham. I then go to my gran's house, a further 36 miles from Birmingham. What simple calculation must I do to show that I have not travelled more than 100 miles?
A bus is hired to take a group of pupils on a trip. The bus seats 48 passengers. If the cost of each fare is £2.80, show that the total cost for the group is less than £150.
A book costs £5.49. If I buy it with a £20 note, do a simple calculation to show that my change is less than £15.
A case of wine contains 12 bottles. In a store room there are 37 cases.
Approximately how many bottles is this? Show how you would do this estimate.
PLENARY: Students to come up to IWB to explain how they have solved problems