Using mental math, the approximate tip to leave for a bill of $81.79, if you tip 15% would be a. $8.20 b. $10.30 c. $12.30 d. $16.40

The easiest way to count 15% from $81.79 is:

1. Since $81.79 is 100%, then if you want to find 10% from this number, you should simply divide by 10. Then 10% from $81.79 is $8.179.

2. Now you know that 10% is $8.179, then 5% is a half of this sum, i.e. $8.179:2=$4.0895

3. 15%=10%+5% and in $ it is $8.179+$4.0895=$12.2685 that is nearly $12.30.

correct choice is C.

d

step-by-step explanation:

hello and welcome!

so, when we see the words "proportional" along with a table, we need to know that we're looking numbers that divide by the same thing.

looking at this table, we simply have to do a trial and error, and divide to see which numbers have the same quotient. if you look at choice a & c, they both have equal quotients for three of the numbers, with one exception, so those can't be the answer. looking at b, there is no similarity, so that can't be it. then, we see d; if you divide all the numbers in the table, you'll see that they all divide by two, which is a proportional relationship, and our answer!

also, always remember that the x will always be the number that goes into y, and somewhere behind this table, is a formula. for this specific table, the formula would be:

since our x-value is being divided by two to get the y-value. and if they were to ask for more numbers in the series, this is the formula you would use to find them.

explanation:

infrared radiation has wavelength in the range between 700 nm and 1 mm. lets' convert these values into scientific notation, keeping in mind that:

let's start from the lower value, we have:

(we moved the dot two places to the left, so we increased the exponent by 2 units, from -9 to -7)

the higher value is:

so, the range of wavelength of infrared radiation is: