Question

Estimate each of the following products by rounding off the first number down
and the second number upwards:
21. 578 X 369
20 472 x 76
I56278​

Answer 1

Answer:

356 x 278

472 x 76

578 x 369

356 x 278

= (300 + 56)(300 - 22)

= 90000 + 300(56 -22) - 56 *22

= 90000 + 300(34) - 56*22

= 90000 + 10200 - 1232

= 98968

472 * 76

= (400 + 72)(100 -24)

= 40000 - 400 * 24 + 100*72 - 24 * 72

= 40000 - 9600 + 7200 - 1728

= 35872

578 * 369

= (500 + 78) * (400 - 31)

= 200000 - 500*31 + 78*400 - 78*31

= 213282