Theory
In ratio questions, the value per item stays the same.
If you know what several items cost together, first work back to 1 item. That gives the value per item.
Then multiply that value by the requested number.
- Work back to 1Divide the total by the known number.
When working back to 1, you find the value of one piece, one pack, or one unit.
Divide the total value by the amount that belongs to it.
If a different amount is asked for after that, multiply the value of 1 by that amount.
- Calculate 1 firstDivide the total value by the amount to find the value of 1.
Dividing means sharing an amount fairly or seeing how many equal groups fit into it.
The first number is the total amount. The second number tells you what you divide by.
Always check whether the division works out exactly. If it does not, you get a decimal number or fraction as the answer.
- Calculate to the requested amountMultiply the value of 1 by the requested amount.
You use multiplication with equal groups.
A × B means that you take the same amount B, A times.Instead of adding again and again, you calculate the product all at once.
- Calculate 1 first
- Calculate to the requested numberMultiply the value of 1 by the requested number.
You use multiplication with equal groups.
A × B means that you take the same amount B, A times.Instead of adding again and again, you calculate the product all at once.
- Work back to 17,5 ÷ 3 = 2,5.
- Calculate to the requested number2,5 × 8 = 20.