Because there are 7 days in a week and 30 days in April, according to the formula 30÷7=42, it can be concluded that there are 4 complete weeks in April, which is 2 days more. Considering that there are five Saturdays and Sundays in April, we can know that the extra two days must be Saturdays and Sundays.

And we can know that April 1 is the same as April 8, April 15, April 22 and April 29. At the same time, because Saturday is before Sunday, April 1 must be Saturday. Only when this condition is met, it will return to Saturday after four full weeks, that is, 28 days, thus becoming a rest.