Question

Which demonstrates a method of finding the product of 79 and 21? A) multiply 79 by 20 then add 1 B) multiply 8 by 21 and subtract 21 C) multiply 9 by 21, then add 70 times 21 D) multiply 10 by 8 and then add 10 times 9

Answer 1

Answer:

(B) multiply 8 by 21 and subtract 21

Answer 2

Answer:

C) multiply 9 by 21, then add 70 times 21

Step-by-step explanation:

The product of 79 and 21 is  $79*21=1659$ (by direct calculation)

We analyze each statement to find out which one is correct

A) multiply 79 by 20 then add 1

evaluated gives

$(79*20)+1=1580+1=1581$

therefore A) is incorrect

B) multiply 8 by 21 and subtract 21

is evaluated as

$(8*21)-21=168-21=147$

option B) is incorrect

C) multiply 9 by 21, then add 70 times 21

evaluated gives

$(9*21)+(70*21)=189+1470=1659$

Therefore option C) is correct

D) multiply 10 by 8 and then add 10 times 9

is

$(10*8)+(10*9)=80+90=170$

option C) is incorrect