Name: _____________
Date: _______________
Select an efficient method for solving a problem: mental estimation, mental
computation, written algorithms, by using a calculator.
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For the next eight problems, select the most appropriate method for solving each one and then solve it.
You may use each method no more than three times.
Show your working out for each problem.
If you choose mental computation or mental estimation, briefly write why you chose that method in your
‘Working out’ section.
You must use each method at last twice.
Example # 1
In Jenny Lou’s, I want to buy three chocolate bars. Each bar costs 9 ¥. How much do I spend?
Circle your choice: mental estimation
mental computation
written algorithms
use a calculator
Working out: -
I know my 3X tables. This is the quickest way for me to solve
this problem.
Answer:
27¥
Example #2
In Jenny Lou’s, I want to buy 25 chocolate bars. Each bar costs 12 ¥. How much do I spend?
Circle your choice: mental estimation
mental computation
written algorithms
use a calculator
Working out: -
25 x 12 =
25
x 10
250
25
x 2
50
OR
any other way of working
this out
300
Answer: -
300¥
Now answer these: 1. The Earth takes 365.25 days to circle the sun in one year. How many days will it take to circle the sun in 1387
years? (Don’t worry about ‘leap years’!)
Circle your choice: mental estimation
mental computation
written algorithms
use a calculator
Working out: -
Answer:
2. For your birthday party, you take your friends to get ice cream. Each ice cream costs 20¥. If you take 10 friends,
how much will you spend?
Circle your choice: mental estimation
mental computation
written algorithms
use a calculator
Working out: -
Answer:
3. Research shows that there are 999,999,999 bicycles in Beijing.
7,256,987 of them are blue, the rest are red. How many red bicycles are there?
Circle your choice: mental estimation
Working out: -
mental computation
written algorithms
use a calculator
Answer:
4. You want to play your new video game for 1½ hours tonight when you get home. You get home at 4.00 pm. It
takes 4 hours to do your homework, have a piano lesson, have dinner with your family, play with your friends, and
take a shower. Do you think you have the time you want to spend on playing your game, if you go to bed at 9.00?
Circle your choice: mental estimation
mental computation
written algorithms
use a calculator
Working out: -
Answer:
5. There are 22 children in each class at WAB. There are five classes in each grade from KG to grade 5 (KG, grade
1, grade 2, grade 3, grade 4, and grade 5). About how many children are there altogether from KG to grade 5 at
WAB?
Circle your choice: mental estimation
mental computation
written algorithms
use a calculator
Working out: -
Answer:
6. You have 50¥. Do you have enough money if you want to buy 3 things that cost 15¥ each?
Circle your choice: mental estimation
Working out: -
mental computation
written algorithms
use a calculator
Answer:
7. Mr. Cowell needs to purchase 135 cans of drink for the Grade 5 social. How many packs of 24 should he get?
Circle your choice: mental estimation
mental computation
written algorithms
use a calculator
Working out: -
Answer:
8. Ms Favilli went to the store last night with 100 rmb. She needed to buy a loaf of bread (12 rmb), a litre of milk
(26 rmb) and lots of chocolate for her class (67 rmb). Did she have enough money?
Circle your choice: mental estimation
Working out: -
Answer:
mental computation
written algorithms
use a calculator