Fatimah has 40 coins. Some of the coins are 50c coins and the rest are 20c coins. The total value is $16.10. How many 50c coins does Fatimah have?

number of 50c = x

number of 20c = y

total coins 40

x +y = 40 (1)

0.5x + 0.2y = 16.10 (2)

from (1) => x = 40 - y

substitute x in (2)

0.5(40 -y) + 0.2y = 16.10

20 - 0.5y + 0.2y = 16.10

-0.3y = -3.9

y = 13

from (1) => x = 27

number of 50c = 27 coins

answer: c, the green line

step-by-step explanation:

there is no black line, eliminate b.

simple interest implies periodic payments, but the red line shows no payments, eliminate d.

simple interest has equal payments. if paid say every day, the graph is about a straight line (actually a stairstep).

the yellow line is not straight, eliminate a.

check: the green line is straight, answer is c.

simple interest with positive interest rate gives a straight line sloping up to the right. green line:

g(t) = $100 + ($200-$100) ÷ (20 years) × (t years)

= $100 + (4%/year) × ($100)(t years)

incidentally, the yellow line curving upward represents continuously compounded interest

y = $100 × 2^(t years / (14 assuming the yellow line hits $200 at 14 years. 2^0 is 1, so y(0) = $100; 2^(14/14) is 2, so y(14) = $200.