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My younger sister (in 5th grade) has a math question about percentages of large numbers. I know how to do it, but I do not think she has learned the method I know. I'm looking for a simple way to find the answer to the following problem.
About 7/10 of the US believe A to be true. 7/10 of the US is 175,104,000. What is the total pop. of the US? (I got 250,148, 571 as the answer)
136,800,000 people believe F to be true. What % of the total pop. believe F to be true? (I got around 55%)
For the first part I did 175,104,000/x = 7/10, then multiplied and divided, which I think is how they're supposed to do it.
For the second question, I divided 136,800,000 by the total pop. then multiplied it by 100. I am wondering if there is an easier way to do that part.
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Why bring in "x" when the problem is simple arithmetic: 7/10 of the US is 175,104,000. What is the total pop. of the US? What you are really asking is HOW a problem is solved, and that will depend very much on HOW it is taught in class, not the way you were taught. This is a major parental problem, and a valid concern, and in my humble opinion there is only one solution:
First do it the way taught in class! Your method might very well be the best and simplest etc, but it is imperative to give one single firm foundation for reason of security in the child. After that, once firmly grasped, you can show optional methods. If you try to show another method or approach at the same time, the child can get utterly confused. So, the ball is in your court, and it's up to you to learn the method taught in class, and not avoid that for your own preference [for now.] I can show you more than one way to divide compound fractions. That is because you are an adult and already have the basis for understanding the two and comparing. If doing it for the first time, as a child, I can not possibly do that without confusing you, unless you have a peculiar talent.
So ...speak to the teacher if you still have any doubt. Don't get too philosophical about it. What matters is the child's best interest, so simply ask how it is done, and follow the textbook/classroom until that's mastered, then you can give other options at a slightly or much later date in an atmosphere of learning.
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