Task Implementation Guide
Grade 5, Unit 6, Lesson 10: Mystery Number: Using understanding of place value to
round decimals in word problems
Possible Student Approach
Teacher Guidance
Correct Answer:
Prompts for discussion​
(with possible student
​
responses​
):
Possible solutions include: .615, .616, .617, .618,
.619 or .620, .621, .622, .623, or .624
Incorrect Answer:
Any number other than: .615, .616, .617, .618,
.619 or .620, .621, .622, .623, or .624.
For a number to round to .62, the digit in the
thousandths place can be less than 5 if the digit
in the hundredths place is 2. If the digit in the
thousandths is 5 or greater, the digit in the
1.
Which place value determines how a decimal
is rounded to a specific place value? ​
(When
rounding a decimal to a specific place value,
the digit directly to the right of that place
value needs to be examined. In the place
value system, each place value plays an
important role. In this task, when rounding to
two hundredths, we need to think about all of
the numbers (written to the thousandths) that
are greater than or less than .620 that round
to .620. Evaluating the digits in both the
thousandths and hundredths places is
important.)
2.
How could this task be solved using a
number line? ​
(Creating a number line
showing the thousandths surrounding .620
would be one way to work through this task.
Values closer to .620 instead of .610 and .630
would be values that round to .620.)
3.
Why were we able to place the 6 in the tenths
place right away? ​
(We know the number is
going to round to .6 when rounded to the
nearest tenth. The digit in the hundredths
place determines which tenth a decimal is
rounded to. Because the decimal rounds to
.6, we know the digit in the hundredths place
needs to be less than 5.)
Prompts for discussion​
(with possible student
​
responses):
1.
How can the digit in the hundredths place be
either 1 or 2? (​
The 1 or 2 in the hundredths
place represents 1 or 2 hundredths. There
are ten thousandths in one hundredth. If the
digit in the hundredths place is a 1, the digit in
the thousandths place must be 5 or greater to
© LearnZillion, Inc. 2015. All Rights Reserved. No part of this document may be
reproduced without LearnZillion's express consent.
hundredths place has to be 1.
round to 2 hundredths. If the digit in the
hundredths place is a 2, the digit in the
thousandths place must be less than 5 to
round to 2 hundredths. The digit in the
thousandths place determines which
hundredths the number is rounded to.)
2.
Why are the values .625, .626, .627, .628, and
.629 incorrect solutions? ​
(These five numbers
are closer to .630 than .620. If we made a
number line showing the thousandths that fall
between .620 and .630, these values would
be closer to .630. These values round
forward to the next hundredth and would not
be correct solutions to this task.)
© LearnZillion, Inc. 2015. All Rights Reserved. No part of this document may be
reproduced without LearnZillion's express consent.