Answer:
The cost of the old ball was $100.
Step-by-step explanation:
The cost of the new ball = $300
The new ball has three times the price of his old ball.
So, let the price of the old ball be = x
As per situation, we get the equation:
Dividing both sides by 3:
=> x = 100
Hence, the cost of the old ball was $100.
Formula for compound interest is
Interest = Amount - Principal
Interest = - P
Where r = rate in percent
t = time in years
For Jaina,
P = $300
r= 7%
t = 3 yrs
So, Interest = - 300
For Tomas
P = $400
r= 4%
t = 3 yrs
So, Interest = - 400
So pair of equations for Jaina and Tomas are
Interest = - 300
Interest = - 400