Here is the OESolution:
Step 1: Understand Question Statement • On Sunday and Monday, only horses and ponies were there in Alexa’s stable.
• On Sunday, the ratio of the number of ponies to the number of horses was 4 :5.
• On Monday, 35 more ponies and horses came to the stable.
• The new ratio of the number of ponies to horses becomes 5:8
• No animals left the stable or died on Sunday and Monday.
We need to find the least number of horses that were in Alexa’s stable on Sunday.
Step 2: Define Methodology • Let’s assume that the numbers of ponies and horses were 4x and 5x respectively, on Sunday.
• Assuming that the m horses came on Monday.
• The total number of horses on Monday = \(5x+m\)
• Total number of animals in stable on Monday = \(9x+35\)
• Since ratio of the number ponies to horses on Monday = \(\frac{5}{8}\)
• The ratio of the number of horses to total animals in stable =\( \frac{8}{8+5}=\frac{8}{13}=\frac{5x+m}{9x+35} \)
• We will solve the above equation to find the value of number of horses on Sunday.
Step 3: Calculate the final answer
• \(\frac{5x+m}{9x+35}=\frac{8}{13} \)
• \(65x+13m=72x+280 \)
⟹\(m=\frac{280+7x}{13} =\frac{280}{13}+\frac{7x}{13}=21+\frac{7}{13}+\frac{7x}{13}=21+\frac{7\left(x+1\right)}{13} ……. (i) \).
Since m is the number of horses, it must be a positive integer.
So, the least value of x for which m is an integer is = \((x+1) = 13⟹x = 12\)
Hence, \(x= 12\) and the least number of horses on Sunday = \(5\ast12=60\)
Thus, the correct answer is O
ption C.