Calculation of Day of the Week

To determine the day of the week for a particular date, we use the following formula:

Day of the week = [(Number of days from a known reference day) mod 7]

Here, the known reference day is 1st January 1900, which was a Monday.

Calculation for 1st July, 1977

To find the number of days between 1st January 1900 and 1st July 1977, we count the number of leap years and non-leap years that have elapsed in between.

Number of non-leap years = 77 - 1 = 76
Number of leap years = (77 - 1) / 4 = 19
Total number of days = (76 x 365) + (19 x 366) + (181 - 1) = 28024

Here, we subtract 1 from the number of days because we only want to count the days from 1st January 1900 to 30th June 1977.

Now, we apply the formula to find the day of the week:

Day of the week = (28024 mod 7) = 5

Therefore, 1st July 1977 was a Friday.

Calculation for 1st July, 1970

To find the day of the week for 1st July 1970, we follow the same procedure as above.

Number of non-leap years = 70 - 1 = 69
Number of leap years = (70 - 1) / 4 = 17
Total number of days = (69 x 365) + (17 x 366) + (182 - 1) = 25567

Here, we add 1 to the number of days because we want to count the day 1st July 1970 as well.

Now, we apply the formula to find the day of the week:

Day of the week = (25568 mod 7) = 3

Therefore, 1st July 1970 was a Wednesday.

Conclusion

Hence, the correct answer is option 'A' - Wednesday.