Question #30e2e

2 Answers
Jul 3, 2017

This is a long way round but demonstrates the technique of conversions.

the difference is #2lbcolor(white)(.) 9 oz#

Explanation:

To do the subtraction both values need to be in the same units. So lets convert them to ounces.

You need to know that #16oz=1^("lb")#

So #4lbcolor(white)(.)5oz" "->" "[4xx16]+5oz=69oz#
So #1lbcolor(white)(.)12oz" "->" "[1xx16]+12oz=28oz#

#69-28=color(red)(41oz)#

As the question uses pounds and ounces we need to use these units in our answer. So we need to know how many pounds there are in 41 oz

#2xx16=color(green)(32) larr" 2 pounds measured in ounces"#
#3xx16=48 larr" Too much"#

So there is 2 lb + remainder in ounces

#color(red)(41)color(green)(-32)=9# as the remainder in ounces

Thus the difference is #2lbcolor(white)(.) 9 oz#

Jul 3, 2017

A different approach but still using conversion.
This is the better of the two methods.

#2lbcolor(white)(.)9oz#

Explanation:

We have:

#lb" "oz#
#4" "5#
#ul(1" "12larr" Subtract")#

Note that 12 is more than 5 so we 'shift' one of the pound into the ounces column. Note that 1 pound id the same as 16 ounces. So the count of ounces in the top line changes from 5 to 5+16=21. The number of pounds in the top line reduces by 1 so it changes from 4 to 3.

#lb" "oz#
#3" "21#
#ul(1" "12larr" Subtract")#
#2" "9#

Giving: #2lbcolor(white)(.)9oz#