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Current time:0:00Total duration:2:35

Dividing fractions by whole numbers: studying

CCSS.Math: ,

Video transcript

Tommy is studying for final exams this weekend he will spend one fifth of the weekend studying what fraction of the weekend will he spend studying for each for each of his four subjects if he spends the same amount of time studying for each subject so the total amount of time he's going to spend studying this weekend is 1/5 of the weekend and he has to divide that into four equal sections and he's going to spend that much time on each subject so he's going to divide this he's going to divide this by four now we've already seen that dividing by a number is the same thing as multiplying by its reciprocal you might say well what's the reciprocal of four we just have to remind yourself that four is the same thing as 4 over 1 so 1/5 divided by 4 over 1 is the same thing as 1/5 times times 1/4 times 1/4 and you could also view this as 1/4 of 1/5 or 1/5 of 1/4 either way but here we multiply our numerators to get 1 and then we multiply our denominators 4 5 5 is 20 so you get one twentieth of the weekend will be spent studying for each subject now let's also try to think about this visually let's imagine that this is his entire weekend and I've divided it into five equal sections and so we already said we already know that the total amount of his weekend spent studying is 1/5 so that's the total amount studying for the weekend is 1/5 now he has to divide this into four equal sections so let's do that he's got it he's got 4 subjects he's gonna spend the same amount of time on each of the 4 subjects so he's going to divide this into 4 equal sections so how much time does he spend on one subject well in each subject that would be this layer that I'm doing in yellow right over here and what is that well that's 1 1 over how many equal sections are there of that size in the weekend well I've just drawn out the grid you had 5 rows and now you have 4 columns so 5 rows times 4 columns you have 20 equal sex 20 equal section so once again looking at it visually he's spending one twentieth of his weekend on each of the four subjects if you have and then if you do this for four subjects that means that his and this whole weekend one-fifth will be spent studying but the question that they're asking he's spending one twentieth of the weekend on each subject