题目内容
仔细观察,选择合适的方法计算.
(1)63+24+37 | (2)65+42+44 | (3)18+36+72 | (4)78+15+85 | (5)28+34+66 |
(6)35+44+56 | (7)232-48-52 | (8)318-63-37 | (9)427-39-27 | (10)385-(78+85) |
(11)63-9-9-9 | (12)500-97-98-99 | (13)700-101-102 | (14)351-(151+56) | (15)49+49+49+49 |
(16)72+54+28+45 | (17)1+2+3+4+5+6+7 | (18)6+17+18+19 | (19)0+2+4+6+8+10+12 | (20)3+6+9+12+15+18+21. |
分析:(1)(2)(3)(4)(5)(6)运用加法结合律简算;
(7)(8)(10)(14)运用减法的性质简算;
(9)(16)运用加法交换律与结合律简算;
(11)把63看作9×7,把-9-9-9看作-9×3,运用乘法分配律简算;
(12)把原式变为500-(100-3)-(100-2)-(100-1),简算即可;
(13)把原式变为700-(100+1)-(100+2),简算即可;
(15)原式变为49×4,然后把49看作50-1,运用乘法分配律简算;
(17)-(20)运用高斯求和公式计算即可.
(7)(8)(10)(14)运用减法的性质简算;
(9)(16)运用加法交换律与结合律简算;
(11)把63看作9×7,把-9-9-9看作-9×3,运用乘法分配律简算;
(12)把原式变为500-(100-3)-(100-2)-(100-1),简算即可;
(13)把原式变为700-(100+1)-(100+2),简算即可;
(15)原式变为49×4,然后把49看作50-1,运用乘法分配律简算;
(17)-(20)运用高斯求和公式计算即可.
解答:解:(1)63+24+37,
=63+24+37,
=100+37,
=137;
(2)65+42+44,
=65+(42+44),
=65+86,
=151;
(3)18+36+72,
=18+72+36,
=90+36,
=126;
(4)78+15+85,
=78+(15+85),
=78+100,
=178;
(5)28+34+66,
=28+(34+66),
=28+00,
=128;
(6)35+44+56,
=35+(44+56),
=35+00,
=135;
(7)232-48-52,
=232-(48+52),
=232-100,
=132;
(8)318-63-37,
=318-(63+37),
=318-100,
=218;
(9)427-39-27,
=427-27-39,
=400-39,
=361;
(10)385-(78+85),
=385-78-85,
=385-85-78,
=300-78,
=222;
(11)63-9-9-9,
=9×7-9×3,
=9×(7-3),
=9×4,
=36;
(12)500-97-98-99,
=500-(100-3)-(100-2)-(100-1),
=200+6,
=206;
(13)700-101-102,
=700-(100+1)-(100+2),
=500-3,
=497;
(14)351-(151+56),
=351-151-56,
=200-56,
=144;
(15)49+49+49+49,
=49×4,
=(50-1)×4,
=200-4,
=196;
(16)72+54+28+45,
=72+28+(54+45),
=100+99,
=199;
(17)1+2+3+4+5+6+7,
=(1+7)×7÷2,
=8×7÷2,
=28;
(18)6+17+18+19,
=6+(20-3)+(20-2)+(20-1),
=6+60-6,
=60;
(19)0+2+4+6+8+10+12,
=(0+12)×7÷2,
=12×7÷2,
=42;
(20)3+6+9+12+15+18+21,
=(3+21)×7÷2,
=24×7÷2,
=84.
=63+24+37,
=100+37,
=137;
(2)65+42+44,
=65+(42+44),
=65+86,
=151;
(3)18+36+72,
=18+72+36,
=90+36,
=126;
(4)78+15+85,
=78+(15+85),
=78+100,
=178;
(5)28+34+66,
=28+(34+66),
=28+00,
=128;
(6)35+44+56,
=35+(44+56),
=35+00,
=135;
(7)232-48-52,
=232-(48+52),
=232-100,
=132;
(8)318-63-37,
=318-(63+37),
=318-100,
=218;
(9)427-39-27,
=427-27-39,
=400-39,
=361;
(10)385-(78+85),
=385-78-85,
=385-85-78,
=300-78,
=222;
(11)63-9-9-9,
=9×7-9×3,
=9×(7-3),
=9×4,
=36;
(12)500-97-98-99,
=500-(100-3)-(100-2)-(100-1),
=200+6,
=206;
(13)700-101-102,
=700-(100+1)-(100+2),
=500-3,
=497;
(14)351-(151+56),
=351-151-56,
=200-56,
=144;
(15)49+49+49+49,
=49×4,
=(50-1)×4,
=200-4,
=196;
(16)72+54+28+45,
=72+28+(54+45),
=100+99,
=199;
(17)1+2+3+4+5+6+7,
=(1+7)×7÷2,
=8×7÷2,
=28;
(18)6+17+18+19,
=6+(20-3)+(20-2)+(20-1),
=6+60-6,
=60;
(19)0+2+4+6+8+10+12,
=(0+12)×7÷2,
=12×7÷2,
=42;
(20)3+6+9+12+15+18+21,
=(3+21)×7÷2,
=24×7÷2,
=84.
点评:完成此题,应注意分析式中数据,运用运算定律或运算技巧,灵活简算.
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仔细观察,选择合适的方法计算.
(1)63+24+37 | (2)65+42+44 | (3)18+36+72 | (4)78+15+85 | (5)28+34+66 |
(6)35+44+56 | (7)232-48-52 | (8)318-63-37 | (9)427-39-27 | (10)385-(78+85) |
(11)63-9-9-9 | (12)500-97-98-99 | (13)700-101-102 | (14)351-(151+56) | (15)49+49+49+49 |
(16)72+54+28+45 | (17)1+2+3+4+5+6+7 | (18)6+17+18+19 | (19)0+2+4+6+8+10+12 | (20)3+6+9+12+15+18+21. |