We don't have the other number, so we must do the reverse operation, which is subtraction. So we have to subtract 27 from 15. 7-5 is 2, and 20-10 is 10. Add those together and you get 12.
Step-by-step explanation: First, convert 0.4 into 4/10. Then, divide the numerator and the denominator by 2. You should get 2/5, which can’t be simplified any more. Voila!
