Answer: 
Step-by-step explanation:
Given
Sample of 12 measurements has a mean of 16.5 and
a sample of 15 measurements has a mean of 18.6
Take
be the mean and no of measurements
and
be the mean and no of measurements in second case

Similarly,

Mean of 27 measurements

Answer:
The algebraic expressions can be presents by words or equivalent expressions, so that its meaning remains same.
Step-by-step explanation:
Different ways to present algebraic expressions without changing their meaning:
1. We can describe the algebraic expressions in words so that its meaning remains same.
For example : 3x+y = Sum of 3 times of an unknown variables x and y.
2. We can describe the algebraic expressions in equivalent expressions, so that its meaning remains same.
For example : 6x+3y = 3(2x+y)
Therefore, the algebraic expressions can be presents by words or equivalent expressions, so that its meaning remains same.
You say to yourself "Self ! This is easy, and I refuse to let it scare me !
I know that 20 dollars minus 2 dollars leaves 18 dollars.
And I know that 20 cows minus 2 cows leaves 18 cows.
And I know that 20 puppies minus 2 puppies leaves 18 puppies.
So it's obvious to me that 20 of anything minus 2 of the same thing
is always 18 of them.
It doesn't matter whether the things are hairbows, goldfish, cars,
CDs, books, or 'x', 'y', or 'z'.
So 20m minus 2m is definitely 18m."