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## Arithmetic

### Course: Arithmetic>Unit 5

Lesson 1: Intro to place value through 1,000

# Intro to place value

Sal introduces place value using a toy with beads (an abacus).  Created by Sal Khan.

## Want to join the conversation?

• Try to extend the logic of this exercise across number bases other than 10. :) Cool video!
• Unary-----------1 for every number.
1
11
111
1111
11111
Thats good for learning to count but not really anything else
Binary----------1 for every power of 2 in other words 2 beads per row
1
10(this is 2 not 1)
11
100
101
Powers do go up fast but powers of 2 are the slowest
Ternary---------1 for every power of 3 or 3 beads per row
1
2
10(3 not 2)
11
12
Quarternary---------1 for every power of 4
Twice as efficeint as binary to express the same thing
Quinary----------1 for every power of 5
and we could go on to base 360 but 360 is a lot of beads.
You know the babylonians used base 60. I find that really interesting. Time in hours:minutes:seconds is also base 60.
• how can one of those be 100
• Shouldn't there be 9 beads in each row?
• At they say that there is ten beads in each row.
They did it because it is easy to find multiples of 10 and the numbers are easy to deal with.
• this did not help so much but would it just be easier to just use exponent to explain
this topic?
• Well, keep in mind that this is a 2nd grade math level concept. For example, if you were a second grader, wouldn't fractions be difficult to learn? I mean, if you have, I don't mean to bring you down or offend any exceedingly intelligent second grader. If your among them, or were, keep up the good work!
• They told me what to do but i kind of stilldont get it
• why do we use place value
• to help represent numbers, using a base 10 system and to count easier and faster.
• what is the ones place?
• The ones place is the first number before a decimal. The numbers could be 1,2,3,4,5,6,7,8,9 or 0. In the number 235, the number 5 is in the ones place. In 14,567, 7 is the number in the ones place.
• I’m ninety persent in second grade
• Nice job Aman, I'm at 100%!
Did you know that a percentage actually means a fraction?
96% means 96 divided by 100!
So when they say "What is 40% of 100", you can solve it by doing 40/100 x 100.
An easier way is to just do (40 x 100) divided by 100.