First, let us decide the numbers that will give 40 as their product.
One set of the possible numbers be 2, 2 and 10.
Now, find decimals which are very close to these numbers.
Subtract 0.01 from one number and add to another number.
Now, let's find the product of 1.99, 2.01 and 9.99.
1.99 × 2.01 = 3.9999
3.9999 × 9.99 = 39.959
≅ 40