PSLE
Risa had a total of 207 red and black beads. She used 27 red beads and 40% of the black beads. After that, the ratio of the number of red beads to black beads Risa had was 10 : 3.

1. What fraction of her black beads did Risa use? Give your answer in the simplest form.
2. How many beads did Risa have in the end?

	Red beads	Black beads	Total
Before	10 u + 27	5 u	15 u + 27
Change	- 27	- 2 u
After	10 u	3 u	13 u
Comparing red beads and black beads in the end	10	3	13

(a)
40% = ⁴⁰₁₀₀ = ²₅

Fraction of her black beads that Risa used = ²₅

(b)
The number of black beads in the end is repeated.
Since the numbers are already the same, we do not need to use LCM to make them the same.

Number of black beads at first = 5 u
Number of red beads at first = 10 u + 27

Total number of beads at first
= 5 u + 10 u + 27
= 15 u + 27

15 u + 27 = 207
15 u = 207 - 27
15 u = 180

1 u = 180 ÷ 15 = 12

Number of black beads in the end = 3 u
Number of red beads in the end = 10 u

Total number of beads in the end
= 10 u + 3 u
= 13 u
= 13 x 12
= 156

Answer(s): (a)²₅; (b) 156