Mathematics 5 curriculum guide 2015 I table of contents acknowledgements

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58
MATHEMATICS 5 CURRICULUM GUIDE 2015
Specific Outcomes
ADDING AND SUBTRACTING DECIMALS
Suggestions for Teaching and Learning
Students will be expected to:
Number
5N11 Demonstrate an 
understanding of addition 
and subtraction of decimals 
(limited to thousandths).
[C, CN, PS, R, V]
5N11.1 Predict sums and 
differences of decimals, using 
estimation strategies.
Students should develop computational fluency with decimal numbers.
In the past, decimal computation was dominated by lining up the 
decimal places. While this is important, for accurate computation a firm 
understanding of place value is needed.
Students should begin by using estimation to predict sums and 
differences. The estimation strategies covered in outcome 5N2 will help 
students determine if their solution is reasonable. 
Jack rode his bike 8.5 km on Monday, and 7.3 km on Tuesday. How far 
did he ride in two days?
Estimates might be similar to:
9 km + 7 km = 16 km (rounding)
8 km + 7 km = 15 km ( front-end estimation or compatible numbers)
When students begin to find exact solutions to sums and differences of 
decimal numbers, they should always be encouraged to compare them to 
their estimates to determine if the calculated answer is reasonable.
5N11.2 Place the decimal point 
in a sum or difference, using 
estimation.
Estimation strategies should also help students determine correct decimal 
placement in a sum or difference.
Ask students to estimate 4.13 + 5.67
They may respond with 4 + 5 = 9 (using front-end estimation) or 
4 + 6 = 10 (using rounding or compatible numbers).
Focus attention on the fact that there are 9 or 10 wholes.
Display the digits of the answer but do not include the decimal:
4.13 + 5.67 = 980 
Ask students: Where does the decimal belong?
They should be able to connect this with their estimate and realize that 
their estimate was nine or ten. Therefore, the decimal must be placed so 
that the solution has about 9 or 10 wholes. The correct response would 
be 9.80.
Similarly with subtraction: Ask students to estimate 87.85 - 78.52.
They may suggest 88 - 79 = 9 (or something close depending on the 
strategy chosen).
The answer without the decimal point is: 87.85-78.52 = 933
Ask students where the decimal goes. According to their estimate the 
answer has to be about nine, so 9.33 is the correct placement.