The average temperature for three days was 19 degrees. What must the temperature be on the fourth day to make the average temperature during the four days 21 degrees?

The average of 3 days temperature was 19 degrees:

[(x+x+x)/3]=19
x+x+x=3*19
x+x+x=57
let assume the three x values are 17, 21 and 19 which equal 57 degrees.
[(17+21+19+x)/4]=21
(57+x)=4*21
57+x=84
x=84-57
x=27
the 4th day temperature must be 27 degrees.

(T1+T2+T3)/3 = 19, T1+T2+T3 = 3*19 = 57. (57+T4)/4 = 21, T4 = 27 Degrees.

27 degrees

To determine the temperature on the fourth day, we need to first calculate the total temperature for the four days by multiplying the average temperature by the number of days.

The average temperature for three days is given as 19 degrees. So, the total temperature for the three days is 19 * 3 = 57 degrees.

To find the temperature on the fourth day, we can use the formula for the average temperature:

Average Temperature = (Total Temperature for All Days) / (Number of Days)

We want the average temperature for the four days to be 21 degrees. We already have the total temperature for the three days as 57 degrees, and the number of days is 4.

So, we can rearrange the formula to find the temperature on the fourth day:

(57 + Fourth Day Temperature) / 4 = 21

To isolate Fourth Day Temperature, we can multiply both sides of the equation by 4:

57 + Fourth Day Temperature = 84

Finally, we can calculate the temperature on the fourth day by subtracting 57 from both sides of the equation:

Fourth Day Temperature = 84 - 57

Fourth Day Temperature = 27 degrees

Therefore, the temperature on the fourth day must be 27 degrees to make the average temperature during the four days 21 degrees.