David saved $175 each month for the first five months and then saved $225 each month for the next five months.
what is the average amount david saved each month?

200
Equation: 175 × 5 + 225 × 5 ÷ 10 = 200
Explanation: to find the average, you add up all the numbers, then divide by how many numbers there are. 

Solve for average amount saved each month?

1st five months saved $175 each for five months.
 175 x 5 = $875
2nd five months saved $225 each for five months.
225 x 5 = $1125
Add both amounts:  $875 + $1125 = 2000
Divide by the number of months which was ten month worth of savings.
 2000/10 = $200 average saved each month