Gauss' method for addition relies on the fact that you can 'pair' certain numbers together. Look at the example:
1+2+3+4+5+6+7+8+9+10
We could manually add all these together from left to right but a clever way to think about this is if we add together the ends of the sum (10+1) we get 11. If we then move one in from the ends and add these (2+9) we also get 11. This means that 1+2+...+9+10 is the same as 11+11+...+11+11.
Because each 2 numbers adds to 11 we know the total number of 11's we have to add together is the length of the sum divided by 2. In our case 5 (10 ÷ 2). We need to add 5 lots of 11 to get our answer. This is the same as 11 × 5 which is easily seen to be 55.
(If you add the 10 numbers together on a calculator you'll see 1+2+3+4+5+6+7+8+9+10 = 55) so this method really makes it a lot quicker.
Looking at your sequence, if we pair the ends together we get 401 (400+1) and we multiply this by the length of the sequence divided by 2. In your case, 200 (400 ÷ 2).
So the sum of all the numbers from 1 to 400 must be 401 × 200 = 80,200.
Remember the steps:
1. Pair the ends together and add them
2. Times this number by the length of the sequence halved
Hope this helps.
Answer:
C. 4.3 cm
Step-by-step explanation:
Since it is a right triangle you can use a²+b²=c² to solve this. Then you subtract 2 from the AC to get AD.
Answer:
−0.125 or - 1/8
Step-by-step explanation:
Answer:
x+18
Step-by-step explanation:
Answer:
Points B and C are opposite
Step-by-step explanation:
0 on the number line marks the center of the number line. To the right on the number line are positive integers and to the left from zero are negative integers.
Points B and C are opposite because they are each half way between 0 and 1 on the right and 0 and -1 on the left
