I think A = 14

A 14

It is like a sudoku puzzle.... The sum of all sides must be 30

Thank you so much Bindhu and Subha for your advise!

U r welcome😊

Whenever you have a qn like this, work systemically. Its always the four operations. Add , subtract, multiply or divide. You cant go wrong

Thanks kim

I think it is 14

14

99/2=49.5 1+99 = 100 49.5 x 100= 4950

thk u

1+99=100 2+98=100 3+97=100 etc... till 48+52=100 49+51=100 So total 49 sets of 100 = 4900, 4900+50=4950

The formula for summation of integers from 1 to N, inclusive is (1 + N) × N/2 For N = 99, (1 + 99) × 99/2 = 50 × 99 = 4950 As highlighted by many contributors, formulas are best understood rather than memorized and applied blindly.

This question was a PSLE question many yrs ago, itz actually a test of number bonds for primary school kids, think they haven't learnt formula...?

How does this formula come about? Imagine a series of numbers 1,2,3,4,5,6,7,8 and 9. What then is the sum of this series? Imagine another one of the said series is available. The first series is placed in a column in ascending order (meaning from lowest to highest) while the second but identical series is placed side-by-side and in descending order. The third column below shows the sum of the elements in each row. 1st 2nd Sum 1 9 10 2 8 10 3 7 10 4 6 10 5 5 10 6 4 10 7 3 10 8 2 10 9 1 10 There are 9 numbers in each series. We can see that the elements in the ascending and descending series in each row add up to 10, which is also the sum of the smallest number in the series (1 ) and the largest number in the series (9 ). There are nine rows, so (1 + 9) × 9 Remember that there are two series involved, so divide by two.... That is how the formula for the summation of whole numbers from 1 to N, inclusive comes about (1 + N) × N/2 With modification, summation of a series not starting from 1, or summation of multiples of say 3 of a series can thus be determined.

If I remember right, the PSLE question on summation was in section A, an MCQ type. The question seeked for the digit in the ones place for the summation of 1 to 97, inclusive.

👍 understood. :) Thanks!

Happy to share, so we can all progress.

thk u everyone

Thank you for a good question.

And this question is in GEP first round for Pri 3

Use ap formula. N(N+1)/2 . 99 X 99+1/2=99 X 100/2 =9900/2=4950

GEP is a misnomer. For the given population size of Singapore, statistically speaking there will not be hundreds of children in each cohort to make the ranks of the naturally gifted. The very fact that the GEP classes across Singapore are filled up, this highlights two main possibilities : that nurturing appears to be effective in turning the naturally ungifted children into gifted ones, or that many students made it into GEP because the filters used to ferret out the gifted are just full of flaws. Having said that, the GEP has its function and it has helped many students, gifted or otherwise accelerate their learning curves. Be that good or bad is open to debate.

Thank you very much ;)

U are most welcomed!

Thank u very much 😀

Thanks Yueh Mei! 👍🙏 this is an awesome page!

(a) The other three factors are 3, 5 and 45. (b) The two numbers are 45 and 180.

9 = 3 × 3, so 3 must be a factor 15 = 3 × 5, so 5 must also be a factor 3 × 3 × 5 = 45, and hence 45 is the final factor, and the smaller of the two numbers. The larger number is hence 4 × 45 = 180

thank u very much :)

You are most welcome. Regards