Question

Tìm a biết: a + a × 2 + a × 3 + a × 4 + … + a × 49 + a × 50 = 12750

Answer 1

Lời giải:

$a+a\times 2+a\times 3+a\times 4+....+a\times 49+a\times 50=12750$

$a\times (1+2+3+4+...+49+50)=12750$

$a\times 50\times 51:2=12750$

$a\times 1275=12750$

$a=12750:1275=10$