Bob, Celia, Sam and Daniel gave money to buy their boss a retirement gift. Sam and Daniel each gave the same amount of money. Celia gave $12 more than Daniel. Bob gave half as much as Celia gave. If the four workers contributed a total of $81, how much did Celia give?

here's the equation: x+x+(x+12)+ 1/2(x+12) =81

combine like terms

(x+x+x+1/2x) + (12+6) = 81

simplify

7/2x +18=

subtract 18 from both sides.

7/2x=63

multiply by reciprocal (aka 2/7)

x=18

18+12=30 so celia gave 30.

Hope this helps!

reduce the friction between its moving parts

step-by-step explanation:

in fact, by reducing the friction between the moving parts of the machine, it is possible to reduce the energy wasted due to this friction; therefore, more input energy is converted into useful work, and this will improve the efficiency of the machine.

answer: median

step-by-step explanation:

the median is the middle value when a data set is ordered from least to greatest