Question

Estimate each of the following products by rounding of the first number downwards
and the second number upwards:
19. 356 x 278
20. 472 x 76
21. 578 x 369
​

Answer 1

Answer:

Step-by-step explanation:

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

Answer 2

Answer:

19 - 356 ×278

356 downward = 300

278 upward = 300

300× 300 = 90000

20 - 472 × 76

472 downward = 400

76 upward = 80

400 × 80 = 32000

21 - 578 × 369

578 downward = 500

369 upward = 400

500 × 400 = 200000