How do I multiply decimal numbers?

Start by multiplying the two numbers as though they didn't have a decimal point (e.g. 2.7*3.6 becomes 27*36 = 972). Now add up how many decimal places were in the original two numbers (e.g. 2.7 and 3.6 have 2 decimal places, 3.45 and 9.2 have 3 decimal places) and give your answer that number of decimal places (e.g. since 2.7 and 3.6 have 2 decimal places, 2.7*3.6 will have 2 decimal places. Calculate 27*36 = 972, then give it 2 decimal places to get 2.7*3.6 = 9.72).

Remember that, in this situation, zeroes should be counted as decimal places. For example: 1.02*4.05. Calculate 102*405 = 41,310. Now notice that 1.02 and 4.05 have 4 decimal places. Therefore, give 41,310 4 decimal places to find that 1.02*4.05 = 4.1310.

Step by step this is layed out as:

1) Multiply without decimal points.

2) Count the number of decimal places in the 2 numbers you're multiplying.

3) Give your answer to part (1) the number of decimal places from part (2).

Seb G. 11 Plus Maths tutor, 13 plus  Maths tutor, A Level Maths tutor...

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