Answer: 5400
In scientific notation it is 5.4 * 10^3
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Work Shown:
n = number of grains of salt
1 grain = 6.48 * 10^(-5) kg = 0.0000648 kg
The exponent of -5 indicates to move the decimal point 5 spots to the left.
n grains = 0.0000648n kg
Set this equal to the stated weight of 0.35 kg and solve for n.
0.0000648n = 0.35
n = 0.35/0.0000648
n = 5401.23456790123
n = 5400
This is when rounding to 2 significant figures. The 2 most significant values are the left-most items 5 and 4. Everything else becomes a 0. These particular zeros aren't significant.
The number 5400 in scientific notation is 5.4 * 10^3