Question

A child building a tower with Blocks uses 15 for the bottom row. Each row has 2 fewer blocks than the previous row. What formula would you use to find the number of blocks in the 5th row?

A)blocks in 5th row =15+(15-1)-2
B)blocks in 5th row=15+(5-1)(-2)
C)blocks in 5th row=15+(5+1)(-2)
D)blocks in 5th row=5+(15-1)(-2)

Answer 1

B)blocks in 5th row=15+(5-1)(-2)

Explanation:

We are given that

Number of block in bottom row=15

Each row has 2 fewer blocks than the previous row

We have to find the formula would you use to find the number of blocks in the 5th row.

Number of blocks in second row=15-2=
`15+1(-2)`

Number of blocks in third row=15-2-2=
`15+2(-2)`

Number of blocks in 4th row=
`15-2-2-2=15+3(-2)`

Number of blocks in 5th row=
`15-2-2-2-2=15+4(-2)`

Therefore, number of block in 5th row

`15+(5-1)(-2)`

This is required formula to find the number of blocks in the 5th row

Hence, option B is true.

B)blocks in 5th row=15+(5-1)(-2)