Singapore math level 2A & 2B – Formula sheet
Unit 10 Mental Calculations
Addition and subtraction can be done mentally by rounding
numbers and breaking up numbers.
Mental addition by rounding numbers
1. Round one of the addends, A, to the nearest ten.
2. Mentally add the rounded number to the other addend, B.
3. Subtract the difference between the rounded number and addend A from the sum.
Mental addition by breaking up numbers
When one of the addends, A, is less than 10,
1. break up the other addend, B, into ones and tens/hundreds.
Example: Break up 364 into 4 and 360.
2. Add the ones to get a sum.
3. Add the sum to the remaining tens/hundreds to get the final answer.
Apply the same method to an addend that is less than 100 or 1,000.
Mental subtraction by rounding numbers
1. Round one of the subtrahends, A, to the nearest ten.
2. Mentally subtract the rounded number from the other subtrahend, B.
3. Add the difference between the rounded number and subtrahend A to the result in 2.
Mental subtraction by breaking up numbers
When one of the subtrahends, A, is less than 10,
1. break up the other subtrahend, B, into ones and tens/hundreds.
Example: Break up 526 into 6 and 520.
2. Subtract the ones to get a result.
3. Add the result in 2 to the remaining tens/hundreds.
Apply the same method to a subtrahend that is less than 100 or 1,000.
Unit 11 Money
Writing dollars and cents
$1 = 100¢
When writing dollars and cents, place a dollar sign ($) in the
front and a decimal point (.) to separate them.
Example: $8.95
When writing dollars without any cents, add 2 zeros after
the decimal point.
Example: $8.00
When writing cents without any dollars, add a zero before
the decimal point.
Example: $0.95
Converting dollars to cents
• Remove the dollar sign ($) and the decimal point (.).
• Place the cent symbol (¢) after the number.
Example: $20.50 = 2,050¢
Converting cents to dollars
• Remove the cent symbol (¢).
• Place the dollar sign ($) before the number.
• Place the decimal point (.) just before the last 2 digits.
Example: 3,000¢ = $30.00
Comparing money
• Compare the dollars of the 2 amounts first.
• If the dollars are the same, compare the cents.
Unit 12 Fractions
In a fraction, each part must be equal.
Examples of a fraction: \[\frac12,\frac25\]and \[\frac88\] .
To make a whole, make sure all denominators are common. All
numerators add up to equal the denominator.
Example: \[\frac28\] and \[\frac68\] make a whole.
Comparing and arranging fractions in order
• When denominators of all fractions are the same, compare their numerators.
The largest fraction has the highest value in the numerator.
Example: \[\frac45, \frac25, \frac15 \] largest
• When numerators of all fractions are the same, compare their denominators.
The largest fraction has the smallest value in the denominator.
Example: \[\frac14, \frac18, \frac1{12} \] largest
This table can be useful when comparing fractions.
Adding and subtracting fractions
• Make sure denominators of all fractions are the same.
• Add and subtract the numerators accordingly.
When one of the subtrahends is a whole, convert the whole into a fraction before subtracting.
Unit 13 Time
There are 24 hours in a day.
1 hour = 60 minutes
Numbers 1 to 12 can be seen on the face of a clock, as well as the hour hand and minute hand.
The minute hand is longer than the hour hand.
When the minute hand moves from one number to another, 5 minutes has passed.
When the hour hand moves from one number to another, 1 hour has passed.
The units of measurement for time are hour (hr.) and minute (min.).
Writing and reading time
We read the time on the clock as three twenty-five.
We write it as 3:25.
The abbreviation A.M. means before noon and P.M. means after noon.
Hence A.M. is used to talk about time between 12 midnight and 11:59 in the morning.
P.M. is used to talk about time between 12 noon and 11:59 at night.
We can find the time before/after a certain time if the duration is given.
Examples: 10:00 A.M. is 1 hr. before 11:00 A.M.
7:00 P.M. is 1 hr. after 6:00 P.M.
9:30 A.M. is 30 min. before 10:00 A.M.
5:30 P.M. is 30 min. after 5:00 P.M.
Unit 14 Volume
The volume of water in a container is the amount of water the container holds.
Comparing volume
• When the water level in 2 identical containers is the same, use the words as much as.
• When the water level in one container is higher than that of the other container, use the words more than.
• When the water level in one container is lower than that of the other container, use the words less than.
The unit of measurement for volume is liter (L) or gallon (gal.).
Unit 15 Graphs
Symbols represent the items in picture graphs.
Note the scales used in picture graphs. The symbol can stand for 1 item, 2 items, or even more.
Picture graphs help organize information for easy interpretation and problem solving.
Unit 16 Lines and Surfaces
Examples of straight lines:
Examples of curves:
Examples of items with only flat surfaces:
Unit 17 Shapes and Patterns
2-dimensional shapes and objects
Examples of different shapes:
These shapes can be used to create a 2-dimensional figure.
An example of a 2-dimensional figure that is made of 2 quarter circles, a square, and a triangle.
3-dimensional objects
Examples of 3-dimensional objects:
These shapes can be used to create a 3-dimensional figure.
An example of a 3-dimensional figure that is made of 2 cubes and a cylinder.
Patterns
Shapes can be used to create a repeated pattern.
An example of a repeated pattern using different shapes:
An example of a repeated pattern using different sizes:
An example of a repeated pattern using different colors:
