
Pls help
Pls help
Figure Number | Number of dots |
1 | 1 |
2 | 1 + 2 |
3 | 1 + 2 + 3 |
4 | 1 + 2 + 3 + 4 |
n | 1 + 2 + 3 + 4 + … + n |
It is good for your child to memorise that formula for 1 + 2 + 3 + 4 + … + n is
n(n + 1) ÷ 2
n(n + 1) ÷ 2 = 120
n(n + 1) = 240
n² + n = 240
Now, √240 = 15.4919…., so the answer should be 15.
Test
15 × 16 = 240
240 ÷ 2 = 120
Therefore, figure 15 has 120 dots.
There is a pattern for this. The figure number is equal to the number of dots in the largest diagonal row.
I used a calculator for this because i did additions to reach 120. I found the answer to be 15 in that way.
There may be other methods, but for me, I used this method which suits me best.
There is a pattern for this. The figure number is equal to the number of dots in the largest diagonal row.
I used a calculator for this because i did additions to reach 120. I found the answer to be 15 in that way.
There may be other methods, but for me, I used this method which suits me best.