PSLE
Zoe had two ribbons of the same length. She cut the first ribbon into equal parts of length 70 cm and to each part she tied 3 pink balls. After that, she cut the second ribbon into equal parts of length 100 cm and to each part she tied 5 black balls. When she finished tying, she counted that there were 20 more black balls than pink balls. How many balls were there altogether?

	First ribbon	Second ribbon	Difference	Total
Length of each part	70 cm	100 cm
Number of balloons tied to each part	3 pink balloons	5 black balloons
LCM	700 cm	700 cm
Number of equal parts	700 ÷ 70 = 10	700 ÷ 100 = 7
Number of balloons for each ribbon per set	10 x 3 = 30	5 x 7 = 35	35 - 30 = 5	30 + 35 = 65

LCM of 70 and 100 = 700

Number of sets of 3 pink balls in a length of 700 cm
= 700 ÷ 70
= 10

Number of pink balls in a length of 700 cm
= 10 x 3
= 30

Number of sets of 5 black balls in a length of 700 cm
= 700 ÷ 100
= 7

Number of black balls in a length of 700 cm
= 7 x 5
= 35

Extra number of black balls in a length of 700 cm
= 35 - 30
= 5

Number of sets of balls
= 20 ÷ 5
= 4

Total number of balls in one set of 700 cm of pink balloons and one set of 700 cm of black balloons
= 30 + 35
= 65

Total number of balls of the two ribbons
= 4 x 65
= 260

Answer(s): 260