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PSLE Mathematics

Question post on Fri, 04/09/2020 10:06am

Pls help

BigDevil · Answer 1 · Post on Sat, 05/09/2020 2:30am

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.

FrankKK · Answer 2 · Post on Fri, 04/09/2020 2:00pm

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.

FrankKK · Answer 3 · Post on Fri, 04/09/2020 2:00pm

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.