Math Is Fun Forum

There are currently 17 separate sections, most of which get used at some time and covering all the types of post that people make.  When a member makes a post it appears straight away on the forum. The moderators have to check regularly to make sure no post is abusive, illegal or otherwise unsuitable for publication. That's a big job and we do this voluntarily. It's called post-moderation meaning the check is done after the post appears.

There's an alternative: pre-moderation. With that, posts don't appear straight away. They are put in a holding area until they are 'passed' as suitable for publication.  Such a system is safer but means members don't get quick responses and cannot have a to and fro chat.

If you add lots of extra subsections it makes the job of post-moderation much, much more laborious. I doubt I've be able to keep up.

The key to making a good post is to decide which section it should appear in and then give it a good title so readers know what it's about.  That has worked well for 19 or so years.  I don't want it to change.

Bob

Yes, that's all you can do.  Momentum must be a vector measure as it has velocity as a component. If the man is accelerating then his momentum is going up.

Bob

hi Fra1990

Welcome to the forum.

You can simplify powers by using the rules for indices. https://www.mathsisfun.com/algebra/exponent-laws.html

phrontister has tidied up your maths notation to make the expression clearer. But is that what you meant?

Another interpretation of what you've posted is:

Please post again, making it clear which is right.

When you've got x and times in an expression you can use a .  for the times to avoid confusion.

Bob

hi mathenjoyer

Welcome to the forum!

Well I'm glad you found an answer.  I cannot! So how about helping me out here. Where did 1.5 come from?

Bob

Material from volcanos doesn't usually reach escape velocity so things probably sort themselves out as stuff falls back to Earth.  Rockets that go into orbit haven't left either and the direction of push is pretty random as the Earth rotates so that seems to sort that out.

If too many rockets go on one way trips to, say, the Moon, then this might widen the Earth Moon distance, especially as the landing would use the Moon's surface for breaking. But if a regular trade in Moon material started up the other way then there's a bigger problem. The increase in the overall weight of the Earth would affect it's rotation. Ho hum for the simple life.

Bob

Does it?  It shouldn't. Those mm measurements are all pretty close so the miles should be too.  But you've got places so close you could walk/swim the distance.

I did it this way. What do you have to multiply 58 by to get 1046. answer =what it has become,  divided by what it was.

multiplier = 1046/58

Bob

ps. Maths is supposed to represent the real world so any answer should pass the 'is it reasonable?' test.

The first number in each sum is decreasing by 1 and the second number is increasing by 1. So I would expect the total to stay constant.

In general if a + b = c  then (a+1) + (b-1) = c and more generally still, (a + n) + (b - n) = c for all n.

Bob

98

Bob

This is why it works:

Positive powers of ten are 10, 100, 1000, etc so make a number bigger.

So if you reduce the value of the numeric part (32.14 becomes 3.214) you need to restore the value with a positive power of ten.

Negative powers of ten are fractional so they make a number smaller.

So if you increase the value of the numeric part (0.0514 becomes 5.14) you need to restore the value with a negative power of ten.

The number of places you have moved the decimal point tells you what power you need.

Bob

Correct.

Bob

That grading method requires that every year an exam is set with exactly the same degree of difficulty.

If the questions are , for example, harder one year then less students will reach the pass marks for each grade.

In the UK grades are not pre-determined. After the marking is complete the chief examiner and other examiners use their experience from previous years to set an appropriate pass mark for that year.

For GCSE the syllabus specifies what a grade F, C and A student should be able to do which makes it easier to decide, after the exam, if the pass marks are being correctly set.

This also enables people to assess whether standards are rising from year to year.

Bob

Correct.

Bob