20/39×7.8

=20/39×78/ 10

=20/39×39/5

=20/5

=4

Score calculation:

Different denominator scores are added and subtracted, and then divided first, that is, using the basic properties of scores, different denominator scores are converted into the same denominator score, the unit of scores is changed without changing the size, and then the offer score can be reduced according to the addition and subtraction of the same denominator score.

Divide a fraction by an integer and the denominator remains the same. If the numerator is not a multiple of an integer, multiply this score by the reciprocal of the integer, and finally the offer score can be reduced.