Answer:
90 pounds
Step-by-step explanation:
We can set up an equation to find their weights.
Let's start by naming Joan's weight x.
Her sister's weight would then be x+10, since Joan weighs 10 pounds less.
To find the average between 2 numbers, you need to add them together, then divide by 2.
<u>So we can set up the following equation:</u>
(x+x+10)/2=85
Now let's isolate x.
We can first multiply both sides by 2.
x+x+10=170
Combine like terms.
2x+10=170
Subtract 10 from both sides.
2x=160
Subtract both sides by 2.
x=80
Joan weighs 80 pounds.
x+10 is her sister's weight.
80+10=90
Joan's older sister weighs 90 pounds.
