Write down the reference amount. Consider the following example: "Bill has $250 in one account. His second account contains an amount that is at a 3 to 1 ratio in relation to the first account." In this case, you would write down 250.
Write down the ratio as a fraction. The first number of the ratio is the numerator (top number), and the second number is the denominator (bottom number). In this example, you would write 3/1.
Set the ratio fraction equal to the reference amount, with the reference amount as the denominator of a fraction. The numerator of this fraction should be "x." In this example, you would write 3/1 = x/250.
Cross multiply to calculate the second account's balance. To cross multiply, multiply the numerator of each fraction times the denominator of the other fraction, leaving the equal sign in the middle. In this case, you would multiply 3 times 250 and 1 times "x," which would leave you with 750 = x (or x = 750). This means that the account balance in this example equals $750.