Answer: 36
Step-by-step explanation:
Given
The ratio of Mary's to Helen's necklaces is 25:9
Mary has 100 necklaces
Suppose Helen has x necklaces
Therefore the ratio can be written like
[tex]\Rightarrow \dfrac{25}{9}=\dfrac{100}{x}\\\\\Rightarrow x=\dfrac{100}{25}\times 9\\\\\Rightarrow x=4\times 9\\\Rightarrow x=36[/tex]
So, Helen has 36 necklaces