A textbook store sold a combined total of 219 history and chemistry textbooks in a week. The number of chemistry textbooks sold was 45 less than the number of history textbooks sold. How many textbooks of each type were sold?

132 history textbooks, 87 chemistry textbooks

Step-by-step explanation:

H = 132,

C = 132 - 45 = 87

87 Chemistry and 132 history textbooks.

Step-by-step explanation:

Let x represent the number of chemistry textbooks that was sold.

Let y represent the number of history textbooks that was sold.

The textbook store sold a combined total of 219 history and chemistry textbooks in a week. This means that

x + y = 219 - - - - - - - - - - - -1

The number of chemistry textbooks sold was 45 less than the number of history textbooks sold. This means that

x = y - 45

Substituting x = y - 45 into equation 1, it becomes

y - 45 + y = 219

2y = 219 + 45 = 264

y = 264/2 = 132

x = y - 45 = 132 - 45

x = 87

the largest number of the four options is 1.8 x 10-2

you have it in scientific notation.

1.80 x 10-6   = 0.00000180

1.80 x 10-4   = 0.000180 (bigger, or "less small", than the former one)

so

1.8 x 10-2       = 0.0180. as you see. the "less small", or the biggest one of them all.

as you have negative exponent, it means you are dividing 1.8 by 100 (i.e. moving the dot towards left, two times).

if you had positive exponent for the scientific notation, power of tenths, you would be multiplying times 100 (moving the dot towards right) as below:

1.8 x (10)2 = 180

so. if you have negative exponent in scientific notation, move the dot toward left. if it is positive, toward right as many times the exponent tells you.