Imperial to metric: stones and pounds to kilograms

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Question 1

Complete the following conversion from imperial to metric units (preferably without the use of a calculator).

A patient reports their weight to be $\var{massst} \text{ st (stones) and } \var{masslb} \text{ lb (pounds)}$ . Find their weight in kilograms correct to one decimal place by using that $1 \text{ st} = 14 \text{ lb}$ and $1 \text{ lb} = 0.4536 \text{ kg}$ .

Weight $=$ Expected answer: kg (1 dec. pl.)

$1 \text{ st} = 14 \text{lb}$ , and so $\var{massst} \text{ st}= \var{massst} \times 14 \text{ lbs} = \var{st2lb} \text{ lbs}$ .

Add on the additional $\var{masslb} \text{ lbs}$ , and the patient's weight in pounds is $\var{totlbs} \text{ lbs}$ .

Given $1 \text{ lb} = 0.4536 \text{ kg}$ , we must have $\var{totlbs} \text{ lbs} = \var{totlbs} \times 0.4536 \text{ kg}$ .

We could use the calculator for this but we should also be able to do it without one.

Without a calculator we determine $\var{totlbs}\times 4536$ (which is $\var{precround(masskg*10000,0)}$ ) and then move the decimal place so we have four decimal places again (that is $\var{masskg}$ ). Once we have done the multiplication we can then round to one decimal place (that is, $\var{onedec}$ ).

$\text{Weight} = \var{masskg}\text{ kg} = \var{onedec} \text{ kg (1 dec. pl)}$

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Imperial to metric: stones and pounds to kilograms

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