A textbook store sold a combined total of 274 psychology and biology textbooks in a week. The number of psychology textbooks sold was 78 more than the number of biology textbooks sold. How many textbooks of each type were sold?

176 psychology textbooks and 98 Biology textbooks were sold.

Step-by-step explanation:

Let x represent the number of psychology textbooks that were sold.

Let y represent the number of biology textbooks that were sold.

textbook store sold a combined total of 274 psychology and biology textbooks in a week. This means that

x + y = 274 - - - - - - - - - - -1

The number of psychology textbooks sold was 78 more than the number of biology textbooks sold. This means that

x = y + 78

Substituting x = y + 78 into equation 1, it becomes

y + 78 + y = 274

2y = 274 - 78

2y = 196

y = 98

x = y + 78 = 98 + 78

x = 176

psychology books sold=173

Biology books sold=95

Step-by-step explanation:

Psychology textbooks sold=p

Biology textbooks sold=b

P+b=274

P-78=b

P+P-78=274

2P-78=274

2P=274+78

2P=352

P=352/2

P=173

Substance P=173 in P-78=b

173-78=b

95=b b=95

or

step-by-step explanation:

we need to solve for 'x' the following equation:  

we have that:

⇒

⇒ ⇒

factorizing, we get that:

  ⇒

then, the solutions are: or

nothing extraneous has been found!