() kg is four fifths less than 40 kg, and one fourth more than 40 kg is () kg
40×(1-4/5)=8
40×(1+1/4)=50.
In the case of one class, the unit 1 is known, multiplication is used. The unit 1 is unknown, division is used
40×(1-4/5)=8
40×(1+1/4)=50.
In the case of one class, the unit 1 is known, multiplication is used. The unit 1 is unknown, division is used