The ratio of red to blue marbles in a bag is 2:5. If there are 65 blue marbles in the bag, how many red marbles are there? Let x represent the number of red marbles. Set up a proportion and cross multiply to solve.

first get the total ratio; 2 + 5 = 7

so the fraction of blue marbles is 5/7

then assume the number of total marbles to be k

then use the expression;

5/7*k = 65

7*5/7 * k = 65*7

5k =455

5/5k = 455/5

k = 91

then calculate the number if red marbles from;

x = 2/7*91

x = 26

Therefore there are 26 red marbles.

-13

step-by-step explanation:

f(x)=2x-5 for f(-4)

f(-4)   means let x=-4

f(-4) = 2(-4) -5

f(-4) =-8-5

      = -13