# Calendar

**This trick must be used when we need to calculate previous date from the given date.**

##### On **10 September 1991** was **Tuesday**. so What was The day on **13 March 1991**.

##### First of all we must Know:

0^{th} odd day=Sunday

1^{th} odd day=Monday

2^{th} odd day=Tuesday

3^{th} odd day=Wednesday

4^{th} odd day=Thursday

5^{th} odd day=Friday

6^{th} odd day=Saturday

### STEP 1 :

First of all we calculate the total number of days between the date **13 March 1991** to **10 September 1991**

Number of Days in1991 | ||
---|---|---|

Mar | 18 | |

Apr | 30 | |

May | 31 | |

Jun | 30 | |

Jul | 31 | |

Aug | 31 | |

Sep | 10 | |

Total No. of Days | 181 |

### STEP 2 :

Now we calculate the **odd day number** and for that we have to divide the total number of days with 7**(1week=7days)** and reminder will be our odd day number.

181 / 7 = 6 odd days **(6 is Reminder)**

### STEP 3 :

As we know given day is **Tuesday** which is
**2 ^{th} odd day**

Let the odd Number associated with the day on **13 March 1991** is 'X'

Tuesday on 10 September 1991 = **2** odd day

so '**X + 6 = 2**'

Now we have to put the value of '**X**' as after dividing '**X + 6**' with '**7**' reminder will be '**2**'

so '**X = 3**' and day is '**Wednesday**'