I need help with this I think I have the right Idea but I ma

I need help with this I think I have the right Idea but I maybe making a simple mistake when entering it into computer that it keeps getting it wrong Carry out the following operations, and express the answer with the appropriate number of significant figures

1. [(281.5×105)(1.300×103)]×2.8931

2. (0.0043×16000.0)+(2811×15)

3. 865×[1257(3.84×102)]

ok so I got this myself and people help i\'ve tried different way as well but i can\'t seem to get the correct sig figs or get it enter

1.[(281.5×105)(1.300×103)]×2.8931 Solve the bracket first. [29557.5-133.9] x 2.8931 29423.6 x 2.8931 = 85125. i think this needs to be two sig figs but not sure because i tried 85 x10^3 but that was still wrong

2. (0.0043×16000.0)+(2811×15) = 68.8 + 42165 = 42234 I think this is two sig figs as well but same problem as the frist

3. 865×[1257(3.84×102)] 3.86 x ( 865 ) = 3338.9 = 3.33 x 10^-3 and I am not sure why this was wrong ?

Solution

1.   [(281.5×105)(1.300×103)]×2.8931

when 281.5 and 105 are multiplied the product is 29557.5.In 281.5 we have 4 significant digits and in 105 we have 3 significant digits.The product cannot have more than least of the significant digits that we multiplied.So the product is 29600 having 3 significant digits.

Similarly 1.300 has 4 significant digits and 103 has 3 significant digits.The product is 133.9.It should be rounded to 3 significant digits.

So its values is 134.

(29600-134)*2.8931

(29466)*2.8931

Now in this we have 5 significant digits in each number.The product is 85248.0846.It should be rounded to 5 significant digits.The answer is 85248.

2. (0.0043×16000.0)+(2811×15)

0.0043 has 2 significant digits and 16000.0 has 6 significant digits.The product is 68.8.If 68.8 is rounded to 2 significant digits the answer is 69.

69+(2811*15)

2811 has 4 significant digits and 15 has 2.

The product is42165.If 42165 is rounded to 2 significant digits the answer is 42000.

69+42000=42069.Here we have 2 and 5 significant.So the final answer is 42000.

3. 865×[1257(3.84×102)]

=865*(1257-392)

=865(865)

748225.

3.84 and 102 when multiplied we get 391.68 which when rounded to 3 significant digits we get 392.