Mark four numbers forming a square in a calendar:



Add the squares of the diagonal pair and find the difference of these sums:

4² + 12² = 160

11² + 5² = 146

160 – 146 = 14

Do this for other four numbers.

Compute the following in head:

68² – 32²

Find out the larger product of each pair below, without actual multiplication.

25 × 75, 26 × 74

Compute the following in head:

Compute the following in head:

201 199

Find out the larger product of each pair below, without actual multiplication.

10.6 × 9.4, 10.4 × 9.6

Find out the larger product of each pair below, without actual multiplication.

76 × 24, 74 × 26

Take nine numbers forming a square in a calendar and mark the four numbers at the corners.

Multiply the diagonal pairs and find the difference of these products.

3 × 19 = 57

17 × 5 = 85

85 – 57 = 28

Explain using algebra, why the difference is always 28 (It is convenient to take the number at the centre as x).

Compute the following differences:

(124 × 76) – (126 × 74)

Compute the following differences:

(125 × 75) – (126 × 74)

Compute the following differences:

(125 × 75) – (126 × 74)