Question

Joan weighs 10 pounds less than her older sister. The average of the two sisters’ weights is 85 pounds. How much does Joan’s older sister weigh?

Answer 1

Joan's older sister weighs 90 pounds

Explanation:

x = older sister

x - 10 = Joan

(x + (x-10))/2 = 85

2x - 10 = 170

2x = 180

x = 90

Answer 2

90 pounds

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.

So we can set up the following equation:

(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.