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Body Mass


This is a level 5 number link activity from the Figure It Out series. It relates to Stage 8 of the Number Framework.

Achievement Objectives:

Achievement Objective: NA5-3: Understand operations on fractions, decimals, percentages, and integers.
AO elaboration and other teaching resources

Specific Learning Outcomes: 

use a calculator to multiply and divide decimals

Required Resource Materials: 
FIO, Link, Number, Book Five, Body Mass, page 10
A calculator

Ensure that the students understand the formula given at the top of the page. They also need to know how to round to one decimal place. In the case of Toline, her BMI works out to be 18.517821, so the students need to know that to round to one decimal place, they should look at the digit in the hundredths column (1).
Given that it is not 5 or more, the BMI rounded to one decimal place is 18.5. In Aroha’s case, however, the BMI of 24.779614 is rounded up to 24.8.
This question provides a good opportunity to reinforce how to use the memory function on a calculator. For example, to calculate Toline’s BMI, students using basic calculators could square her height and enter this amount in memory. They could then enter her mass, press ÷ , recall from memory the squared height MR , and press = . With a scientific calculator, they could enter her mass, press ÷ , enter her height, press x2 to square the height, and then press = .
As an extension, you could discuss the notion of “range”. The idea of range is especially important when estimating any kind of measure (for example, “I think it was between 4 metres and 5 metres long”; “I should be home between 3.30 p.m. and 4 p.m.”), but it is also important in different aspects of health (for example,
an acceptable blood pressure ranges from 80–90 on the lower reading and 120–130 on the upper reading). You could also use the statistics for the students’ height, mass, and BMI to discuss range. For example, “The height of the students is between 1.30 metres and 1.63 metres. What height might most students of this age be?”

Answers to Activity

a. Toline 18.5
b. Steve 22.3
c. Pānia 20.2
d. Josh 19.8
e. Mei Ling 21.5
f. Aroha 24.8
g. Matiu 19.6
h. George 24.8