Thread: need assistance on algebra word problem

Maria is working on the multiplication problem 38*25. Maria says, 4 times 25 is 100, so 40 time 25 is 1000. Now take away 2, so the answer is 998.

Is Maria's method correct or not? If it is correct, write equations that incorporate Maria's work and then show why it's correct. If Maria's reasoning is not correct, work with the portions that are right to correct Maria's work and write a string of equations that corresponds to your corrected method for calculating 38*25. Write your equations in the following form:


38*25=some expression
=some expression
.
.
.

Green 11

it is not correct.

use the distributive property ax(b+c) = ab+ac
in your case 25x38=25x(40-2) =25x40-2x25= 1000 - 50 = 950 the correct answer.

Thank you MINOANMAN.

Originally Posted by green11

Maria is working on the multiplication problem 38*25. Maria says, 4 times 25 is 100, so 40 time 25 is 1000. Now take away 2, so the answer is 998.

Is Maria's method correct or not? If it is correct, write equations that incorporate Maria's work and then show why it's correct. If Maria's reasoning is not correct, work with the portions that are right to correct Maria's work and write a string of equations that corresponds to your corrected method for calculating 38*25. Write your equations in the following form:


38*25=some expression
=some expression
.
.
.

Maria has the right idea, just flawed execution. Since she's done 40x25 = 1000, she thinks that's 2 too many. But it's really 2x25 too many. So she should really be doing 1000 - 50 = 950.

This follows immediately from the distributive law.

38 x 25 = (40 - 2) x 25 = 40 x 25 - 2 x 25.