可以幫我解答對嗎?有2題不會?

3.
A
= 0.0064 - 4*10^(-5)
= 6.4*10^(-3) - 4*10^(-5)
= 6.4*10^(-3) - 4*10^(-2)*10^(-3)
= [ 6.4 - 4*10^(-2) ] * 10^(-3)
= ( 6.4 - 0.04 ) * 10^(-3)
= 6.36 * 10^(-3)

因此, a = 6.36 , b = - 3
a + b = 3.36
a - b = 6.36 - ( - 3 ) = 9.36
故選 ( C ) ..... Ans

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4.
( 2.7*10^6 + 7*10^5 ) ÷ 10^4
= 2.7*10^6÷10^4 + 7*10^5÷10^4 , 分配律
= 2.7*10^2 + 7*10
= 270 + 70
= 340
選 ( A ) ..... Ans

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