Answer:
145 letters were sent to Harry on Friday because it was his birthday.
Step-by-step explanation:
A postal worker is tasked with delivering mail to a large apartment complex.
The worker keeps track of the number of letters sent to each apartment on a daily basis.
On Friday, the worker notices that Harry's apartment has received significantly more mail than usual.
Upon further investigation, the worker discovers that Harry's birthday is on Friday, and his friends and family have sent him a large number of congratulatory letters.
Day Number of letters sent
Monday 120
Tuesday 100
Wednesday 135
Thursday 110
Friday 145
The number of letters sent on Friday is 25% more than the average of the previous days. To calculate this, we first need to find the average number of letters sent on the previous days:
(120 + 100 + 135 + 110) / 4 = 116.25
Next, we multiply the average number of letters sent by 1.25 to find the number of letters sent on Friday:
116.25 * 1.25 = 145.31
Since we cannot send fractions of letters, we round up to the nearest whole number:
145.31 ≈ 145
Thus, 145 letters were sent to Harry on Friday.