Question

Anna has been studying a type of bacteria that triples every month. Originally, there were 4 bacterial cells. She wants to know how many there will be after 15 months. Which equation should she use?. . a15 = 4(3)(15). . a15 = 4(3)15. . a15 = 4(3)15 − 1. . a15 = 4(3)(15 − 1). @perl . @DarkBlueChocobo

Answer 1

Answer:

Option A

Explanation:

The initial number of bacteria's is equal to $4$

This number get tripled every month which means after one month  the number of bacteria's will be $4 * 3$

After two months the number of bacteria's will be $(4 * 3)*3$

After three months the number of bacteria's will be $((4 * 3)*3)*3$

i,e after three months total number of bacteria's is equal to $= 4* (3)^3$

Thus, after three months total number of bacteria's is equal to $= 4* (3)^15$

Hence, option A is correct

Answer 2

Answer:

$a(15)=4(3)^{15}$

Explanation:

Given,

Original number of bacterial cell = 4,

Also, the number of bacterial cell triples every month,

So, the number of bacteria after one month = 3 × 4 = 4(3)

After two months = 3 × 4(3) = 4(3)²,

After three months = 3 × 4(3)² = 4(3)³,

......................................................... , so on,

Thus, the number of bacterial cell after 15 months,

$a(x)=4(3)^x$

For 15 months, x = 15,

Hence, the number of bacterial cells after 15 months,

$a(15)=4(3)^{15}$

Which is the required equation she should use.