The cash price of the bike is

Step 1: Calculate the hire purchase downpayment
The hire purchase price (down payment) is 25% of the cash price

Step 2:Calculate the total money paid for the 10 monthly installments
The total money for the installments will be calculated as

Where,

By substituting the values, we will have

Step 3: Calculate the Hire purchase price
The hire purchase price will be calculated using the formula below

By substituting the values above in the formula, we will have

Step 4: Calculate the interest by paying using hire purchase

By substituting the values,
we will have

Step 5:Calculate the interest as a percent of the cash price
To calculate the interest as the percent of the cash price, we will use the formula below

By substituting the values, we will have

Hence,
The final answer is = 50%