Question Video: Detecting the Wrong Digit in a Multiplication Sentence and Finding the Correct One

Look at this multiplication with an error in the answer: 34 × 4 = 126. Which digit in the answer is wrong and needs to be replaced to make the answer correct? Write the correct answer.

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Video Transcript

Look at this multiplication with an error in the answer: 34 multiplied by four equals 126. Which digit in the answer is wrong and needs to be replaced to make the answer correct? Write the correct answer.

In this question, we have to calculate 34 multiplied by four to find the correct answer. We know that one of the digits in the answer given is incorrect. So let’s calculate the answer. When we multiply a two-digit number by a one-digit number using the standard written method, we always start by multiplying the ones first. We know the number 34 has four ones, and we need to multiply them by four. Four times four is 16. We can write the six in the ones column. And we need to regroup 10 of our ones and exchange them for one 10.

Next, we need to multiply the tens. We got three 10s, and we need to multiply them by four. We know that three times four is 12, so three 10s multiplied by four gives us 12 10s. And we need to add the one that we regrouped earlier. 12 10s plus one more 10 gives us a total of 13 10s. We can write three 10s in the tens column and regroup 10 of our tens for 100. So 34 multiplied by four is 136.

So the digit in the calculation we were given, which is incorrect, is the tens digit. It looks like whoever did the calculation forgot to add the 10 that we’d regrouped. So the digit which is wrong is the two. We need to replace that with a three to make the answer correct. The correct answer should be 136 not 126. We found the error in the calculation by working out 34 multiplied by four using the standard written method. First, we multiplied the ones and regrouped. Then we multiplied the tens. The digit which is wrong is the two, which needs to be replaced with a three. And the correct answer is 136.

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