56. Сумма двух чисел равна 800. Как изменится сумма, если одно слагаемое увеличим на 50, другое уменьшим на 70?

let a and b be two numbers. we are given that \( a + b = 800 \).

if we increase the first number by 50, it becomes \( a + 50 \). if we decrease the second number by 70, it becomes \( b - 70 \).

the new sum will be \( (a + 50) + (b - 70) \).

we can rearrange the terms: \( a + b + 50 - 70 \).

since we know \( a + b = 800 \), we substitute this into the expression: \( 800 + 50 - 70 \).

now, we perform the arithmetic: \( 800 + 50 = 850 \), and \( 850 - 70 = 780 \).

the new sum is \( 780 \).

to find out how the sum changed, we compare the new sum to the original sum:

change in sum = new sum - original sum

change in sum = \( 780 - 800 \)

change in sum = \( -20 \)

this means the sum decreased by 20.

Ответ: Сумма уменьшится на 20.