PSLE
Ivory had two strings of the same length. She cut the first string into equal parts of length 40 cm and to each part she tied 2 brown balls. After that, she cut the second string into equal parts of length 50 cm and to each part she tied 5 green balls. When she finished tying, she counted that there were 30 more green balls than brown balls. How many balls were there altogether?

	First string	Second string	Difference	Total
Length of each part	40 cm	50 cm
Number of balloons tied to each part	2 brown balloons	5 green balloons
LCM	200 cm	200 cm
Number of equal parts	200 ÷ 40 = 5	200 ÷ 50 = 4
Number of balloons for each string per set	5 x 2 = 10	5 x 4 = 20	20 - 10 = 10	10 + 20 = 30

LCM of 40 and 50 = 200

Number of sets of 2 brown balls in a length of 200 cm
= 200 ÷ 40
= 5

Number of brown balls in a length of 200 cm
= 5 x 2
= 10

Number of sets of 5 green balls in a length of 200 cm
= 200 ÷ 50
= 4

Number of green balls in a length of 200 cm
= 4 x 5
= 20

Extra number of green balls in a length of 200 cm
= 20 - 10
= 10

Number of sets of balls
= 30 ÷ 10
= 3

Total number of balls in one set of 200 cm of brown balloons and one set of 200 cm of green balloons
= 10 + 20
= 30

Total number of balls of the two strings
= 3 x 30
= 90

Answer(s): 90