∵已知需求出384X25等于多少
X × Y = Z,即X = Z ÷ Y
∴384 × 25
= 384 × (20 + 5)
= 384 × 20 + 384 × 5
= 7680 + 1920
= 9600
经检验,384 = 9600 ÷ 25符合题意
答:384X25等于9600
S = 3+6+12...+384 (1)2S =6+12+...+384+ 768 (2)
(2)-(1)
S = 768 -3
=765
3+6+12...+384 = S =765
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