Weight: A woman gets on a scale with her baby and her dog.

KingAce

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Oct 12, 2006
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PROBLEM: A woman gets on a scale with her baby and her dog. The scale reads 170 pounds. The woman weighs a hundred pounds more than the sum of the baby's and the dog's weight. The dog weighs 60% less than the baby. Find all their weights.

SOLVING:
Knowing that the woman weighs 100 lbs more than the sum of the baby's and the dog's weight, I assumed that the baby + dog's weight was 70 lbs total and the woman's was therefore 100 lbs. To the gets the dog's weight, I simply set up a proportion (40/100 = x/70) because the dog weighs 60% less than the baby and found that the dog weighed 28 pounds. Next, I subtracted 28 from 70 to get the baby's weight, 42 lbs. and finally added 100 lbs (woman's weight) to make sure it added up to 170lbs. It did, but am I correct? It seems like the way I solved this problem was to simple to get the right answer.
 
You can't assume the dog and baby's weight is 70 lbs.

All 3 weigh 170 lbs: \(\displaystyle W+B+D=170\)

The woman weighs 100 lbs more than the dog and baby:\(\displaystyle B+D+100=W\)

The dog weighs 60% less than the baby: \(\displaystyle 0.4B=D\)

There are 3 equations with three unknowns. Solve the system:

\(\displaystyle W+B+D=170\\B+D+100=W\\0.4B=D\)
 
Thanks. To get my answer, I set up the equation w + b + d = 170 and -w + b + d = -100 to cancel out "w". This gave me the equation 2b + 2d = 70 and plugged this back into the original equations. (my works very messy, so I'm not quite sure what I did at the moment) Anyway, I got the woman's weight equals 135 lbs. Next, I knew b + d = 35, and 40% (dog's weight in regards to baby's) of 35 is 14. So the dog's weight was 14 lbs. and the baby's weight equals 21 lbs (simply found last variable "b" I needed)

IS THIS CORRECT?
 
You're a little mixed up. You took 40% od the baby AND dogs weight.

Let's back sub and get:

\(\displaystyle B+0.4B+100+B+0.4B=170\)

\(\displaystyle 2.8B=70\)

\(\displaystyle B=25\)

The baby weighs 25 lbs.

40% of 25 is 10 lbs for the dogs weight

The woman does(as you said)weigh 135 lbs

135+25+10=170.........check

The dog weighs 60% less than the baby:

25-.6(25)=10.........check
 
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