Question

Câu 15. (1,0 điểm) Tính bằng cách hợp lí.

a) 21 . 169 + ($-$69) . 21;

b) 21 . ($-$25) . ($-$3) . ($-$4).

Answer 1

a) 21 . 169 + (−69) . 21;
= 21 . [169 + (-69)
= 21 . 100 = 2100
b) 21 . (−25) . (−3) . (−4).
= [21 . (-3)] . [(-25) . (-4)]
= (-63) . 100 = -6300

Answer 2

a) =2100

b) = -6300

Answer 3

a) 21 . 169 + ($-$69) . 21

= 21 . [169 + ($-$69)]

= 21 . 100 = 2 100.

b) 21 . ($-$25) . ($-$3) . ($-$4)

= [21 . ($-$3)] . [($-$25) . ($-$4)]

= ($-$63) . 100 = $-$6 300.

Answer 4

a) 21.169 +(-69) .21                                                                   b) 21.(- 25). (- 3 ).(- 4)

=21.169 - 69. 21

=21.(169-69)

=21. 100= 2100

Answer 5

a)21.169+(-69).21

=21.[169+(-69)]

=21.[100]

=21000

b)21.(-25).(-3).(-4)

= [21.(-3)].[(-25).(-4)]

=[21.(-3)].[100]

=[-63].[100]

=-6300

Answer 6

a) 21 . 169 + ($-$69) . 21

= 21 . [169 + ($-$69)]

= 21 . 100 = 2 100.

b) 21 . ($-$25) . ($-$3) . ($-$4)

= [21 . ($-$3)] . [($-$25) . ($-$4)]

= ($-$63) . 100 = $-$6 300.

Answer 7

a) 21 . 169 + (−69) . 21;
= 21 . [169 + (-69)
= 21 . 100 = 2100
b) 21 . (−25) . (−3) . (−4).
= [21 . (-3)] . [(-25) . (-4)]
= (-63) . 100 = -6300

Answer 8

a) 21 . 169 + (−$-$69) . 21

= 21 . [169 + (−$-$69)]

= 21 . 100 = 2 100.

b) 21 . (−$-$25) . (−$-$3) . (−$-$4)

= [21 . (−$-$3)] . [(−$-$25) . (−$-$4)]

= (−$-$63) . 100 = −$-$6 300.

Answer 9

a,2100

b,-6300