I went out today to shop and found myself in my car musing. Hmmm, musing about how much I use my mental maths everyday.
Today I used these mental maths strategies:
- I bought two cakes at $3.99 each. I rounded up the $3.99 to $4.00 and then I doubled the $4.00 to get my estimated total of $8.00. Then I subtracted 2 cents to get my grand total of $7.98 but the store rounded the total up and charged me $8.00 anyway.
- Then I went to a bookstore. I had a gift voucher for $54.00 to spend, so I was in heaven – a bookstore and a voucher! I bought a book for $49.00 and another book for $7.95.
- This is what my brain did:
- I rounded up the $7.95 to $8.00;
- I added this to the $49.00 by using my mental maths strategy of bridging through ten. You increase the $49.00 to $50.00 (adding $1.00 from my $8.00 which left me with $7.00);
- I added the $50.00 and $7.00 together and got an estimated total of $57.00;
- My actual total was $56.95 (remember I rounded up the $7.95 book to $8.00 so I had to subtract 5 cents).
- There is a much faster way of calculating the total of my two books but I want to see if you can work it out.
So please try to answer the following:
- What was the difference between my voucher and the cost of my purchases? Remember to use your $ sign in your answer.
- Tell me something you used your mental maths for today OR demonstrate another way to solve my maths problem at the bookstore.
From Ms Thomsett (click on the mental maths link to see the wordle art cloud)