Roger puts 8 pennies to his bank. Then he added 7 pennies and 25 pennies to his bank. How many pennies does he have in all?

The correct answer is: 40

Roger puts 8 pennies to his bank. Then he added 7 pennies and 25 pennies to his bank.
Total pennies = 8 + 7 + 25
To find partial sums add the digits in tens place and ones place seperately.
Partial sum of 8 + 7 + 25
Step 1 : Add digits in tens and ones place seperately:
08
+ 07

_____
15
Step 2: Partial sum of 15 + 25

10                                    05
+ 20                   and        + 05

_____                             ______
30                                        10

Thus, the sum of 15 + 25 are 30 + 10 = 40.

So, Roger has 40 pennies in all.