Question

Christopher tried this number trick
-write down ur street number
-multiply by 2
-add number of days in a week
-multiply by 50
-add the last two digits of ur phone number
-subtract number of days in a year
-add 15

Determine which line the error occurs
n represent any street number
1) 2n Multiply by 2
2) 2n+7 Days in a week
3) 100n+7 Multiply by 50
p represent last two numbers of phone number
4) 100n+7+p Add phone digits
5) 100n+p-358 Subtract days in a year
6) 100n+p-343 Add 15

Answer 1

The following steps are OK:
 1) 2n Multiply by 2
 2) 2n + 7 Days in a week
 For this case the error occurs in the next step:
 3) 100n + 7 Multiply by 50
 The correct procedure is:
 3) (2n + 7) * 50 = 100n + 350
 answer:
 line the error occurs is:
 3) 100n + 7 Multiply by 50

Answer 2

The error occurs at step 3 when 2n + 7 is multiplied by 50. The result should have 100n + 350 which should be used for further calculations. But in step 3, it shows 100n +7 which indicates the multiplication with 50 influenced only the first variable 2n and not the second one which was 7. Hence the calculation error occurred in step 3.